121 lines
4.6 KiB
Markdown
121 lines
4.6 KiB
Markdown
# browser-headers
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> Compatibility Layer for the Headers class
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[](https://travis-ci.org/improbable-eng/js-browser-headers)
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[](https://www.npmjs.com/package/browser-headers)
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[](LICENSE)
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The [Headers](https://fetch.spec.whatwg.org/#headers-class) class defined in the [fetch spec](https://fetch.spec.whatwg.org/) has been implemented slightly differently across browser vendors at the time of writing (Feb 2017).
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This package intends to provide a wrapper for the `Headers` class to ensure a consistent API and provides headers parsing from CLRF-delimited strings.
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This package is written in TypeScript, but is designed to be used just as easily by JavaScript projects.
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## Installation
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via npm:
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```bash
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$ npm install browser-headers
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```
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## Browser Support
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This library is tested against Chrome, Safari, Firefox, Opera, Edge, IE 10 and IE 9.
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## API
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```js
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import BrowserHeaders from 'browser-headers';
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const headers = new BrowserHeaders({
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"content-type": "application/json",
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"my-header": ["value-one","value-two"]
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});
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headers.forEach((key, values) => {
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console.log(key, values);
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});
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// Output:
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// "content-type", ["application/json"]
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// "my-header", ["value-one","value-two"]
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```
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The `BrowserHeaders` class has the following methods:
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#### constructor(init: Headers | {[key: string]: string|string[]} | Map<string,string|string[]> | string | BrowserHeaders, options: {splitValues: boolean}): string[]
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`init` can be one of:
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* An instance of `Headers`
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* A CLRF-delimited string (e.g. `key-a: one\r\nkey-b: two`)
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* An instance of `BrowserHeaders`
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* An object consisting of `string->(string|string[])` (e.g. `{"key-a":["one","two"],"key-b":"three"}`)
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* A `Map<string, string|string[]>`
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The constructor takes an additional optional `options` parameter of `{ splitValues: boolean = false }`, where
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`splitValues` defines whether the header values should be split by comma (`,`) into separate strings - this is useful
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to unify the `.append` functionality of `Headers` implementations (see the warning at the end of this README).
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`splitValues` should be used with caution and defaults to `false` because it might split what is actually a single
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logical value that contained a `,`.
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#### .get(key: string): string[]
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Returns all of the values for that header `key` as an array
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#### .forEach(callback: (key: string, values: string[]) => void): void
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Invokes the provided callback with each key and it's associated values as an array
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#### .set(key: string, values: string|string[]): void
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Overwrites the `key` with the value(s) specified.
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#### .append(key: string, values: string|string[]): void
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Appends the value(s) to specified `key`.
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#### .delete(key: string, value: string): void
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If the `value` is specified:
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Removes the specified `value` from the `key` if it is present.
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Otherwise:
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Removes all values for the `key` if it is present.
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#### .has(key: string, value?: string): boolean
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If the value is specified:
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Returns true if the `key` contains the corresponding `value`.
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Otherwise:
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Returns true if the `key` has at least one value.
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#### .appendFromString(str: string): void
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Appends the headers defined in the provided CLRF-delimited string (e.g. `key-a: one\r\nkey-b: two`)
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#### .toHeaders(): Headers
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Returns an instance of the browser's `Headers` class. This will throw an exception if the current browser does not have
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the `Headers` class.
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## Warning about `.append` in native `Headers`
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The `.append` function of the `Headers` class differs significantly between browsers.
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Some browsers concatenate the values with `", "` or just `","` and others actually maintain the individual values such that
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they can return later return an array. There is a constructor option (see above: `splitValues`) that can be enabled to
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attempt to parse these concatenated strings back into individual values.
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```js
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const headers = new Headers();
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headers.append("key-A", "one");
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headers.append("key-A", "two");
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const keyA = headers.get("key-A"); // or .getAll depending on the browser
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console.log(typeof keyA);
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console.log(keyA);
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// Output in Edge 14:
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// string
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// one, two
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// Output in Safari 10:
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// string
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// one,two
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// Output in Chrome 56:
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// object
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// ["one", "two"]
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```
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