305 lines
12 KiB
Markdown
305 lines
12 KiB
Markdown
# magic-string
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<a href="https://github.com/Rich-Harris/magic-string/actions/workflows/test.yml">
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<img src="https://img.shields.io/github/actions/workflow/status/Rich-Harris/magic-string/test.yml"
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alt="build status">
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</a>
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<a href="https://npmjs.org/package/magic-string">
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<img src="https://img.shields.io/npm/v/magic-string.svg"
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alt="npm version">
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</a>
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<a href="https://github.com/Rich-Harris/magic-string/blob/master/LICENSE.md">
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<img src="https://img.shields.io/npm/l/magic-string.svg"
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alt="license">
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</a>
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Suppose you have some source code. You want to make some light modifications to it - replacing a few characters here and there, wrapping it with a header and footer, etc - and ideally you'd like to generate a [source map](https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/) at the end of it. You've thought about using something like [recast](https://github.com/benjamn/recast) (which allows you to generate an AST from some JavaScript, manipulate it, and reprint it with a sourcemap without losing your comments and formatting), but it seems like overkill for your needs (or maybe the source code isn't JavaScript).
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Your requirements are, frankly, rather niche. But they're requirements that I also have, and for which I made magic-string. It's a small, fast utility for manipulating strings and generating sourcemaps.
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## Installation
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magic-string works in both node.js and browser environments. For node, install with npm:
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```bash
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npm i magic-string
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```
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To use in browser, grab the [magic-string.umd.js](https://unpkg.com/magic-string/dist/magic-string.umd.js) file and add it to your page:
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```html
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<script src='magic-string.umd.js'></script>
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```
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(It also works with various module systems, if you prefer that sort of thing - it has a dependency on [vlq](https://github.com/Rich-Harris/vlq).)
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## Usage
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These examples assume you're in node.js, or something similar:
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```js
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import MagicString from 'magic-string';
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import fs from 'fs'
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const s = new MagicString('problems = 99');
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s.update(0, 8, 'answer');
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s.toString(); // 'answer = 99'
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s.update(11, 13, '42'); // character indices always refer to the original string
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s.toString(); // 'answer = 42'
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s.prepend('var ').append(';'); // most methods are chainable
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s.toString(); // 'var answer = 42;'
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const map = s.generateMap({
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source: 'source.js',
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file: 'converted.js.map',
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includeContent: true
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}); // generates a v3 sourcemap
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fs.writeFileSync('converted.js', s.toString());
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fs.writeFileSync('converted.js.map', map.toString());
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```
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You can pass an options argument:
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```js
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const s = new MagicString(someCode, {
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// these options will be used if you later call `bundle.addSource( s )` - see below
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filename: 'foo.js',
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indentExclusionRanges: [/*...*/],
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// mark source as ignore in DevTools, see below #Bundling
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ignoreList: false
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});
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```
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## Methods
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### s.addSourcemapLocation( index )
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Adds the specified character index (with respect to the original string) to sourcemap mappings, if `hires` is `false` (see below).
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### s.append( content )
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Appends the specified content to the end of the string. Returns `this`.
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### s.appendLeft( index, content )
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Appends the specified `content` at the `index` in the original string. If a range *ending* with `index` is subsequently moved, the insert will be moved with it. Returns `this`. See also `s.prependLeft(...)`.
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### s.appendRight( index, content )
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Appends the specified `content` at the `index` in the original string. If a range *starting* with `index` is subsequently moved, the insert will be moved with it. Returns `this`. See also `s.prependRight(...)`.
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### s.clone()
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Does what you'd expect.
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### s.generateDecodedMap( options )
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Generates a sourcemap object with raw mappings in array form, rather than encoded as a string. See `generateMap` documentation below for options details. Useful if you need to manipulate the sourcemap further, but most of the time you will use `generateMap` instead.
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### s.generateMap( options )
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Generates a [version 3 sourcemap](https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit). All options are, well, optional:
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* `file` - the filename where you plan to write the sourcemap
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* `source` - the filename of the file containing the original source
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* `includeContent` - whether to include the original content in the map's `sourcesContent` array
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* `hires` - whether the mapping should be high-resolution. Hi-res mappings map every single character, meaning (for example) your devtools will always be able to pinpoint the exact location of function calls and so on. With lo-res mappings, devtools may only be able to identify the correct line - but they're quicker to generate and less bulky. You can also set `"boundary"` to generate a semi-hi-res mappings segmented per word boundary instead of per character, suitable for string semantics that are separated by words. If sourcemap locations have been specified with `s.addSourcemapLocation()`, they will be used here.
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The returned sourcemap has two (non-enumerable) methods attached for convenience:
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* `toString` - returns the equivalent of `JSON.stringify(map)`
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* `toUrl` - returns a DataURI containing the sourcemap. Useful for doing this sort of thing:
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```js
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code += '\n//# sourceMappingURL=' + map.toUrl();
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```
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### s.hasChanged()
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Indicates if the string has been changed.
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### s.indent( prefix[, options] )
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Prefixes each line of the string with `prefix`. If `prefix` is not supplied, the indentation will be guessed from the original content, falling back to a single tab character. Returns `this`.
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The `options` argument can have an `exclude` property, which is an array of `[start, end]` character ranges. These ranges will be excluded from the indentation - useful for (e.g.) multiline strings.
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### s.insertLeft( index, content )
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**DEPRECATED** since 0.17 – use `s.appendLeft(...)` instead
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### s.insertRight( index, content )
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**DEPRECATED** since 0.17 – use `s.prependRight(...)` instead
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### s.isEmpty()
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Returns true if the resulting source is empty (disregarding white space).
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### s.locate( index )
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**DEPRECATED** since 0.10 – see [#30](https://github.com/Rich-Harris/magic-string/pull/30)
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### s.locateOrigin( index )
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**DEPRECATED** since 0.10 – see [#30](https://github.com/Rich-Harris/magic-string/pull/30)
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### s.move( start, end, index )
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Moves the characters from `start` and `end` to `index`. Returns `this`.
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### s.overwrite( start, end, content[, options] )
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Replaces the characters from `start` to `end` with `content`, along with the appended/prepended content in that range. The same restrictions as `s.remove()` apply. Returns `this`.
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The fourth argument is optional. It can have a `storeName` property — if `true`, the original name will be stored for later inclusion in a sourcemap's `names` array — and a `contentOnly` property which determines whether only the content is overwritten, or anything that was appended/prepended to the range as well.
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It may be preferred to use `s.update(...)` instead if you wish to avoid overwriting the appended/prepended content.
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### s.prepend( content )
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Prepends the string with the specified content. Returns `this`.
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### s.prependLeft ( index, content )
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Same as `s.appendLeft(...)`, except that the inserted content will go *before* any previous appends or prepends at `index`
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### s.prependRight ( index, content )
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Same as `s.appendRight(...)`, except that the inserted content will go *before* any previous appends or prepends at `index`
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### s.replace( regexpOrString, substitution )
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String replacement with RegExp or string. When using a RegExp, replacer function is also supported. Returns `this`.
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```ts
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import MagicString from 'magic-string'
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const s = new MagicString(source)
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s.replace('foo', 'bar')
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s.replace(/foo/g, 'bar')
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s.replace(/(\w)(\d+)/g, (_, $1, $2) => $1.toUpperCase() + $2)
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```
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The differences from [`String.replace`]((https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replace)):
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- It will always match against the **original string**
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- It mutates the magic string state (use `.clone()` to be immutable)
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### s.replaceAll( regexpOrString, substitution )
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Same as `s.replace`, but replace all matched strings instead of just one.
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If `substitution` is a regex, then it must have the global (`g`) flag set, or a `TypeError` is thrown. Matches the behavior of the builtin [`String.property.replaceAll`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replaceAll).
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### s.remove( start, end )
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Removes the characters from `start` to `end` (of the original string, **not** the generated string). Removing the same content twice, or making removals that partially overlap, will cause an error. Returns `this`.
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### s.reset( start, end )
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Resets the characters from `start` to `end` (of the original string, **not** the generated string).
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It can be used to restore previously removed characters and discard unwanted changes.
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### s.slice( start, end )
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Returns the content of the generated string that corresponds to the slice between `start` and `end` of the original string. Throws error if the indices are for characters that were already removed.
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### s.snip( start, end )
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Returns a clone of `s`, with all content before the `start` and `end` characters of the original string removed.
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### s.toString()
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Returns the generated string.
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### s.trim([ charType ])
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Trims content matching `charType` (defaults to `\s`, i.e. whitespace) from the start and end. Returns `this`.
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### s.trimStart([ charType ])
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Trims content matching `charType` (defaults to `\s`, i.e. whitespace) from the start. Returns `this`.
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### s.trimEnd([ charType ])
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Trims content matching `charType` (defaults to `\s`, i.e. whitespace) from the end. Returns `this`.
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### s.trimLines()
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Removes empty lines from the start and end. Returns `this`.
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### s.update( start, end, content[, options] )
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Replaces the characters from `start` to `end` with `content`. The same restrictions as `s.remove()` apply. Returns `this`.
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The fourth argument is optional. It can have a `storeName` property — if `true`, the original name will be stored for later inclusion in a sourcemap's `names` array — and an `overwrite` property which defaults to `false` and determines whether anything that was appended/prepended to the range will be overwritten along with the original content.
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`s.update(start, end, content)` is equivalent to `s.overwrite(start, end, content, { contentOnly: true })`.
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## Bundling
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To concatenate several sources, use `MagicString.Bundle`:
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```js
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const bundle = new MagicString.Bundle();
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bundle.addSource({
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filename: 'foo.js',
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content: new MagicString('var answer = 42;')
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});
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bundle.addSource({
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filename: 'bar.js',
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content: new MagicString('console.log( answer )')
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});
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// Sources can be marked as ignore-listed, which provides a hint to debuggers
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// to not step into this code and also don't show the source files depending
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// on user preferences.
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bundle.addSource({
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filename: 'some-3rdparty-library.js',
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content: new MagicString('function myLib(){}'),
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ignoreList: false // <--
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})
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// Advanced: a source can include an `indentExclusionRanges` property
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// alongside `filename` and `content`. This will be passed to `s.indent()`
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// - see documentation above
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bundle.indent() // optionally, pass an indent string, otherwise it will be guessed
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.prepend('(function () {\n')
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.append('}());');
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bundle.toString();
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// (function () {
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// var answer = 42;
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// console.log( answer );
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// }());
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// options are as per `s.generateMap()` above
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const map = bundle.generateMap({
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file: 'bundle.js',
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includeContent: true,
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hires: true
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});
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```
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As an alternative syntax, if you a) don't have `filename` or `indentExclusionRanges` options, or b) passed those in when you used `new MagicString(...)`, you can simply pass the `MagicString` instance itself:
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```js
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const bundle = new MagicString.Bundle();
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const source = new MagicString(someCode, {
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filename: 'foo.js'
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});
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bundle.addSource(source);
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```
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## License
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MIT
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