Function $interpolate

test/angular/1.2/angular.js:8868–8959

* @ngdoc service * @name $interpolate * @kind function * * @requires $parse * @requires $sce * * @description * * Compiles a string with markup into an interpolation function. This service is used by the * HTML ng.$compile $compile service fo

(text, mustHaveExpression, trustedContext)

     *
     */
    function $interpolate(text, mustHaveExpression, trustedContext) {
      var startIndex,
          endIndex,
          index = 0,
          parts = [],
          length = text.length,
          hasInterpolation = false,
          fn,
          exp,
          concat = [];

      while(index < length) {
        if ( ((startIndex = text.indexOf(startSymbol, index)) != -1) &&
             ((endIndex = text.indexOf(endSymbol, startIndex + startSymbolLength)) != -1) ) {
          (index != startIndex) && parts.push(text.substring(index, startIndex));
          parts.push(fn = $parse(exp = text.substring(startIndex + startSymbolLength, endIndex)));
          fn.exp = exp;
          index = endIndex + endSymbolLength;
          hasInterpolation = true;
        } else {
          // we did not find anything, so we have to add the remainder to the parts array
          (index != length) && parts.push(text.substring(index));
          index = length;
        }
      }

      if (!(length = parts.length)) {
        // we added, nothing, must have been an empty string.
        parts.push('');
        length = 1;
      }

      // Concatenating expressions makes it hard to reason about whether some combination of
      // concatenated values are unsafe to use and could easily lead to XSS.  By requiring that a
      // single expression be used for iframe[src], object[src], etc., we ensure that the value
      // that's used is assigned or constructed by some JS code somewhere that is more testable or
      // make it obvious that you bound the value to some user controlled value.  This helps reduce
      // the load when auditing for XSS issues.
      if (trustedContext && parts.length > 1) {
          throw $interpolateMinErr('noconcat',
              "Error while interpolating: {0}\nStrict Contextual Escaping disallows " +
              "interpolations that concatenate multiple expressions when a trusted value is " +
              "required.  See http://docs.angularjs.org/api/ng.$sce", text);
      }

      if (!mustHaveExpression  || hasInterpolation) {
        concat.length = length;
        fn = function(context) {
          try {
            for(var i = 0, ii = length, part; i<ii; i++) {
              if (typeof (part = parts[i]) == 'function') {
                part = part(context);
                if (trustedContext) {
                  part = $sce.getTrusted(trustedContext, part);
                } else {
                  part = $sce.valueOf(part);
                }
                if (part == null) { // null || undefined