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- # magic-string
- <a href="https://github.com/Rich-Harris/magic-string/actions/workflows/test.yml">
- <img src="https://img.shields.io/github/actions/workflow/status/Rich-Harris/magic-string/test.yml"
- alt="build status">
- </a>
- <a href="https://npmjs.org/package/magic-string">
- <img src="https://img.shields.io/npm/v/magic-string.svg"
- alt="npm version">
- </a>
- <a href="https://github.com/Rich-Harris/magic-string/blob/master/LICENSE.md">
- <img src="https://img.shields.io/npm/l/magic-string.svg"
- alt="license">
- </a>
- 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).
- 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.
- ## Installation
- magic-string works in both node.js and browser environments. For node, install with npm:
- ```bash
- npm i magic-string
- ```
- 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:
- ```html
- <script src="magic-string.umd.js"></script>
- ```
- (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).)
- ## Usage
- These examples assume you're in node.js, or something similar:
- ```js
- import MagicString from 'magic-string';
- import fs from 'fs';
- const s = new MagicString('problems = 99');
- s.update(0, 8, 'answer');
- s.toString(); // 'answer = 99'
- s.update(11, 13, '42'); // character indices always refer to the original string
- s.toString(); // 'answer = 42'
- s.prepend('var ').append(';'); // most methods are chainable
- s.toString(); // 'var answer = 42;'
- const map = s.generateMap({
- source: 'source.js',
- file: 'converted.js.map',
- includeContent: true,
- }); // generates a v3 sourcemap
- fs.writeFileSync('converted.js', s.toString());
- fs.writeFileSync('converted.js.map', map.toString());
- ```
- You can pass an options argument:
- ```js
- const s = new MagicString(someCode, {
- // these options will be used if you later call `bundle.addSource( s )` - see below
- filename: 'foo.js',
- indentExclusionRanges: [
- /*...*/
- ],
- // mark source as ignore in DevTools, see below #Bundling
- ignoreList: false,
- // adjust the incoming position - see below
- offset: 0,
- });
- ```
- ## Properties
- ### s.offset
- Sets the offset property to adjust the incoming position for the following APIs: `slice`, `update`, `overwrite`, `appendLeft`, `prependLeft`, `appendRight`, `prependRight`, `move`, `reset`, and `remove`.
- Example usage:
- ```ts
- const s = new MagicString('hello world', { offset: 0 });
- s.offset = 6;
- s.slice() === 'world';
- ```
- ## Methods
- ### s.addSourcemapLocation( index )
- Adds the specified character index (with respect to the original string) to sourcemap mappings, if `hires` is `false` (see below).
- ### s.append( content )
- Appends the specified content to the end of the string. Returns `this`.
- ### s.appendLeft( index, content )
- 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(...)`.
- ### s.appendRight( index, content )
- 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(...)`.
- ### s.clone()
- Does what you'd expect.
- ### s.generateDecodedMap( options )
- 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.
- ### s.generateMap( options )
- Generates a [version 3 sourcemap](https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit). All options are, well, optional:
- - `file` - the filename where you plan to write the sourcemap
- - `source` - the filename of the file containing the original source
- - `includeContent` - whether to include the original content in the map's `sourcesContent` array
- - `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.
- The returned sourcemap has two (non-enumerable) methods attached for convenience:
- - `toString` - returns the equivalent of `JSON.stringify(map)`
- - `toUrl` - returns a DataURI containing the sourcemap. Useful for doing this sort of thing:
- ```js
- code += '\n//# sourceMappingURL=' + map.toUrl();
- ```
- ### s.hasChanged()
- Indicates if the string has been changed.
- ### s.indent( prefix[, options] )
- 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`.
- 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.
- ### s.insertLeft( index, content )
- **DEPRECATED** since 0.17 – use `s.appendLeft(...)` instead
- ### s.insertRight( index, content )
- **DEPRECATED** since 0.17 – use `s.prependRight(...)` instead
- ### s.isEmpty()
- Returns true if the resulting source is empty (disregarding white space).
- ### s.locate( index )
- **DEPRECATED** since 0.10 – see [#30](https://github.com/Rich-Harris/magic-string/pull/30)
- ### s.locateOrigin( index )
- **DEPRECATED** since 0.10 – see [#30](https://github.com/Rich-Harris/magic-string/pull/30)
- ### s.move( start, end, index )
- Moves the characters from `start` and `end` to `index`. Returns `this`.
- ### s.overwrite( start, end, content[, options] )
- 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`.
- 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.
- It may be preferred to use `s.update(...)` instead if you wish to avoid overwriting the appended/prepended content.
- ### s.prepend( content )
- Prepends the string with the specified content. Returns `this`.
- ### s.prependLeft ( index, content )
- Same as `s.appendLeft(...)`, except that the inserted content will go _before_ any previous appends or prepends at `index`
- ### s.prependRight ( index, content )
- Same as `s.appendRight(...)`, except that the inserted content will go _before_ any previous appends or prepends at `index`
- ### s.replace( regexpOrString, substitution )
- String replacement with RegExp or string. When using a RegExp, replacer function is also supported. Returns `this`.
- ```ts
- import MagicString from 'magic-string';
- const s = new MagicString(source);
- s.replace('foo', 'bar');
- s.replace(/foo/g, 'bar');
- s.replace(/(\w)(\d+)/g, (_, $1, $2) => $1.toUpperCase() + $2);
- ```
- The differences from [`String.replace`](<(https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replace)>):
- - It will always match against the **original string**
- - It mutates the magic string state (use `.clone()` to be immutable)
- ### s.replaceAll( regexpOrString, substitution )
- Same as `s.replace`, but replace all matched strings instead of just one.
- If `regexpOrString` 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). Returns `this`.
- ### s.remove( start, end )
- 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`.
- ### s.reset( start, end )
- Resets the characters from `start` to `end` (of the original string, **not** the generated string).
- It can be used to restore previously removed characters and discard unwanted changes.
- ### s.slice( start, end )
- 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.
- ### s.snip( start, end )
- Returns a clone of `s`, with all content before the `start` and `end` characters of the original string removed.
- ### s.toString()
- Returns the generated string.
- ### s.trim([ charType ])
- Trims content matching `charType` (defaults to `\s`, i.e. whitespace) from the start and end. Returns `this`.
- ### s.trimStart([ charType ])
- Trims content matching `charType` (defaults to `\s`, i.e. whitespace) from the start. Returns `this`.
- ### s.trimEnd([ charType ])
- Trims content matching `charType` (defaults to `\s`, i.e. whitespace) from the end. Returns `this`.
- ### s.trimLines()
- Removes empty lines from the start and end. Returns `this`.
- ### s.update( start, end, content[, options] )
- Replaces the characters from `start` to `end` with `content`. The same restrictions as `s.remove()` apply. Returns `this`.
- 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.
- `s.update(start, end, content)` is equivalent to `s.overwrite(start, end, content, { contentOnly: true })`.
- ## Bundling
- To concatenate several sources, use `MagicString.Bundle`:
- ```js
- const bundle = new MagicString.Bundle();
- bundle.addSource({
- filename: 'foo.js',
- content: new MagicString('var answer = 42;'),
- });
- bundle.addSource({
- filename: 'bar.js',
- content: new MagicString('console.log( answer )'),
- });
- // Sources can be marked as ignore-listed, which provides a hint to debuggers
- // to not step into this code and also don't show the source files depending
- // on user preferences.
- bundle.addSource({
- filename: 'some-3rdparty-library.js',
- content: new MagicString('function myLib(){}'),
- ignoreList: false, // <--
- });
- // Advanced: a source can include an `indentExclusionRanges` property
- // alongside `filename` and `content`. This will be passed to `s.indent()`
- // - see documentation above
- bundle
- .indent() // optionally, pass an indent string, otherwise it will be guessed
- .prepend('(function () {\n')
- .append('}());');
- bundle.toString();
- // (function () {
- // var answer = 42;
- // console.log( answer );
- // }());
- // options are as per `s.generateMap()` above
- const map = bundle.generateMap({
- file: 'bundle.js',
- includeContent: true,
- hires: true,
- });
- ```
- 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:
- ```js
- const bundle = new MagicString.Bundle();
- const source = new MagicString(someCode, {
- filename: 'foo.js',
- });
- bundle.addSource(source);
- ```
- ## License
- MIT
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