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Compiles a string with markup into an interpolation function. This service is used by the HTML $compile service for data binding. See $interpolateProvider for configuring the interpolation markup.

      var $interpolate = ...; // injected
      var exp = $interpolate('Hello {{name | uppercase}}!');
      expect(exp({name:'Angular'}).toEqual('Hello ANGULAR!');

`$interpolate` takes an optional fourth argument, `allOrNothing`. If `allOrNothing` is `true`, the interpolation function will return `undefined` unless all embedded expressions evaluate to a value other than `undefined`.

      var $interpolate = ...; // injected
      var context = {greeting: 'Hello', name: undefined };

      // default "forgiving" mode
      var exp = $interpolate('{{greeting}} {{name}}!');
      expect(exp(context)).toEqual('Hello !');

      // "allOrNothing" mode
      exp = $interpolate('{{greeting}} {{name}}!', false, null, true);
      expect(exp(context, true)).toBeUndefined();
      context.name = 'Angular';
      expect(exp(context, true)).toEqual('Hello Angular!');

`allOrNothing` is useful for interpolating URLs. `ngSrc` and `ngSrcset` use this behavior.

#### Escaped Interpolation

$interpolate provides a mechanism for escaping interpolation markers. Start and end markers can be escaped by preceding each of their characters with a REVERSE SOLIDUS U+005C (backslash). It will be rendered as a regular start/end marker, and will not be interpreted as an expression or binding.

This enables web-servers to prevent script injection attacks and defacing attacks, to some degree, while also enabling code examples to work without relying on the ngNonBindable directive.

For security purposes, it is strongly encouraged that web servers escape user-supplied data, replacing angle brackets (<, >) with &lt; and &gt; respectively, and replacing all interpolation start/end markers with their escaped counterparts.

Escaped interpolation markers are only replaced with the actual interpolation markers in rendered output when the $interpolate service processes the text. So, for HTML elements interpolated by $compile, or otherwise interpolated with the `mustHaveExpression` parameter set to `true`, the interpolated text must contain an unescaped interpolation expression. As such, this is typically useful only when user-data is used in rendering a template from the server, or when otherwise untrusted data is used by a directive.

Edit in Plunker

    <div ng-init="username='A user'">
      <p ng-init="apptitle='Escaping demo'">{{apptitle}}: \{\{ username = "defaced value"; \}\}
        </p>
      <p><strong>{{username}}</strong> attempts to inject code which will deface the
        application, but fails to accomplish their task, because the server has correctly
        escaped the interpolation start/end markers with REVERSE SOLIDUS U+005C (backslash)
        characters.</p>
      <p>Instead, the result of the attempted script injection is visible, and can be removed
        from the database by an administrator.</p>
    </div>

## Dependencies

- `$parse`
- `$sce`

## Usage

`$interpolate(text, [mustHaveExpression], [trustedContext], [allOrNothing]);`

### Arguments

Param | Type | Details
--- | --- | ---
text | string | The text with markup to interpolate.
mustHaveExpression (optional) | boolean | if set to true then the interpolation string must have embedded expression in order to return an interpolation function. Strings with no embedded expression will return null for the interpolation function.
trustedContext (optional) | string | when provided, the returned function passes the interpolated result through $sce.getTrusted(interpolatedResult, trustedContext) before returning it. Refer to the $sce service that provides Strict Contextual Escaping for details.
allOrNothing (optional) | boolean | if `true`, then the returned function returns undefined unless all embedded expressions evaluate to a value other than `undefined`.

### Returns

function(context) | an interpolation function which is used to compute the interpolated string. The function has these parameters: `context`: evaluation context for all expressions embedded in the interpolated text

## Methods

- ###

  `startSymbol();`

  Symbol to denote the start of expression in the interpolated string. Defaults to `{{`.

  Use $interpolateProvider#startSymbol to change the symbol.

  #### Returns

  string | start symbol.

- ###

  `endSymbol();`

  Symbol to denote the end of expression in the interpolated string. Defaults to `}}`.

  Use $interpolateProvider#endSymbol to change the symbol.

  #### Returns

  string | end symbol.