Add a benchmark extension.

chrome/test/data/extensions/samples/benchmark/jst/jsevalcontext.js

+// Copyright 2006 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+// implied. See the License for the specific language governing
+// permissions and limitations under the License.
+/**
+ * Author: Steffen Meschkat <mesch@google.com>
+ *
+ * @fileoverview This class is used to evaluate expressions in a local
+ * context. Used by JstProcessor.
+ */
+
+
+/**
+ * Names of special variables defined by the jstemplate evaluation
+ * context. These can be used in js expression in jstemplate
+ * attributes.
+ */
+var VAR_index = '$index';
+var VAR_count = '$count';
+var VAR_this = '$this';
+var VAR_context = '$context';
+var VAR_top = '$top';
+
+
+/**
+ * The name of the global variable which holds the value to be returned if
+ * context evaluation results in an error. 
+ * Use JsEvalContext.setGlobal(GLOB_default, value) to set this.
+ */
+var GLOB_default = '$default';
+
+
+/**
+ * Un-inlined literals, to avoid object creation in IE6. TODO(mesch):
+ * So far, these are only used here, but we could use them thoughout
+ * the code and thus move them to constants.js.
+ */
+var CHAR_colon = ':';
+var REGEXP_semicolon = /\s*;\s*/;
+
+
+/**
+ * See constructor_()
+ * @param {Object|null} opt_data
+ * @param {Object} opt_parent
+ * @constructor
+ */
+function JsEvalContext(opt_data, opt_parent) {
+  this.constructor_.apply(this, arguments);
+}
+
+/**
+ * Context for processing a jstemplate. The context contains a context
+ * object, whose properties can be referred to in jstemplate
+ * expressions, and it holds the locally defined variables.
+ *
+ * @param {Object|null} opt_data The context object. Null if no context.
+ *
+ * @param {Object} opt_parent The parent context, from which local
+ * variables are inherited. Normally the context object of the parent
+ * context is the object whose property the parent object is. Null for the
+ * context of the root object.
+ */
+JsEvalContext.prototype.constructor_ = function(opt_data, opt_parent) {
+  var me = this;
+
+  /**
+   * The context for variable definitions in which the jstemplate
+   * expressions are evaluated. Other than for the local context,
+   * which replaces the parent context, variable definitions of the
+   * parent are inherited. The special variable $this points to data_.
+   *
+   * If this instance is recycled from the cache, then the property is
+   * already initialized.
+   *
+   * @type {Object}
+   */
+  if (!me.vars_) {
+    me.vars_ = {};
+  }
+  if (opt_parent) {
+    // If there is a parent node, inherit local variables from the
+    // parent.
+    copyProperties(me.vars_, opt_parent.vars_);
+  } else {
+    // If a root node, inherit global symbols. Since every parent
+    // chain has a root with no parent, global variables will be
+    // present in the case above too. This means that globals can be
+    // overridden by locals, as it should be.
+    copyProperties(me.vars_, JsEvalContext.globals_);
+  }
+
+  /**
+   * The current context object is assigned to the special variable
+   * $this so it is possible to use it in expressions.
+   * @type Object
+   */
+  me.vars_[VAR_this] = opt_data;
+
+  /**
+   * The entire context structure is exposed as a variable so it can be
+   * passed to javascript invocations through jseval.
+   */
+  me.vars_[VAR_context] = me;
+
+  /**
+   * The local context of the input data in which the jstemplate
+   * expressions are evaluated. Notice that this is usually an Object,
+   * but it can also be a scalar value (and then still the expression
+   * $this can be used to refer to it). Notice this can even be value,
+   * undefined or null. Hence, we have to protect jsexec() from using
+   * undefined or null, yet we want $this to reflect the true value of
+   * the current context. Thus we assign the original value to $this,
+   * above, but for the expression context we replace null and
+   * undefined by the empty string.
+   *
+   * @type {Object|null}
+   */
+  me.data_ = getDefaultObject(opt_data, STRING_empty);
+
+  if (!opt_parent) {
+    // If this is a top-level context, create a variable reference to the data
+    // to allow for  accessing top-level properties of the original context
+    // data from child contexts.
+    me.vars_[VAR_top] = me.data_;
+  }
+};
+
+
+/**
+ * A map of globally defined symbols. Every instance of JsExprContext
+ * inherits them in its vars_.
+ * @type Object
+ */
+JsEvalContext.globals_ = {}
+
+
+/**
+ * Sets a global symbol. It will be available like a variable in every
+ * JsEvalContext instance. This is intended mainly to register
+ * immutable global objects, such as functions, at load time, and not
+ * to add global data at runtime. I.e. the same objections as to
+ * global variables in general apply also here. (Hence the name
+ * "global", and not "global var".)
+ * @param {string} name
+ * @param {Object|null} value
+ */
+JsEvalContext.setGlobal = function(name, value) {
+  JsEvalContext.globals_[name] = value;
+};
+
+
+/**
+ * Set the default value to be returned if context evaluation results in an 
+ * error. (This can occur if a non-existent value was requested). 
+ */
+JsEvalContext.setGlobal(GLOB_default, null);
+
+
+/**
+ * A cache to reuse JsEvalContext instances. (IE6 perf)
+ *
+ * @type Array.<JsEvalContext>
+ */
+JsEvalContext.recycledInstances_ = [];
+
+
+/**
+ * A factory to create a JsEvalContext instance, possibly reusing
+ * one from recycledInstances_. (IE6 perf)
+ *
+ * @param {Object} opt_data
+ * @param {JsEvalContext} opt_parent
+ * @return {JsEvalContext}
+ */
+JsEvalContext.create = function(opt_data, opt_parent) {
+  if (jsLength(JsEvalContext.recycledInstances_) > 0) {
+    var instance = JsEvalContext.recycledInstances_.pop();
+    JsEvalContext.call(instance, opt_data, opt_parent);
+    return instance;
+  } else {
+    return new JsEvalContext(opt_data, opt_parent);
+  }
+};
+
+
+/**
+ * Recycle a used JsEvalContext instance, so we can avoid creating one
+ * the next time we need one. (IE6 perf)
+ *
+ * @param {JsEvalContext} instance
+ */
+JsEvalContext.recycle = function(instance) {
+  for (var i in instance.vars_) {
+    // NOTE(mesch): We avoid object creation here. (IE6 perf)
+    delete instance.vars_[i];
+  }
+  instance.data_ = null;
+  JsEvalContext.recycledInstances_.push(instance);
+};
+
+
+/**
+ * Executes a function created using jsEvalToFunction() in the context
+ * of vars, data, and template.
+ *
+ * @param {Function} exprFunction A javascript function created from
+ * a jstemplate attribute value.
+ *
+ * @param {Element} template DOM node of the template.
+ *
+ * @return {Object|null} The value of the expression from which
+ * exprFunction was created in the current js expression context and
+ * the context of template.
+ */
+JsEvalContext.prototype.jsexec = function(exprFunction, template) {
+  try {
+    return exprFunction.call(template, this.vars_, this.data_);
+  } catch (e) {
+    log('jsexec EXCEPTION: ' + e + ' at ' + template +
+        ' with ' + exprFunction);
+    return JsEvalContext.globals_[GLOB_default];
+  }
+};
+
+
+/**
+ * Clones the current context for a new context object. The cloned
+ * context has the data object as its context object and the current
+ * context as its parent context. It also sets the $index variable to
+ * the given value. This value usually is the position of the data
+ * object in a list for which a template is instantiated multiply.
+ *
+ * @param {Object} data The new context object.
+ *
+ * @param {number} index Position of the new context when multiply
+ * instantiated. (See implementation of jstSelect().)
+ * 
+ * @param {number} count The total number of contexts that were multiply
+ * instantiated. (See implementation of jstSelect().)
+ *
+ * @return {JsEvalContext}
+ */
+JsEvalContext.prototype.clone = function(data, index, count) {
+  var ret = JsEvalContext.create(data, this);
+  ret.setVariable(VAR_index, index);
+  ret.setVariable(VAR_count, count);
+  return ret;
+};
+
+
+/**
+ * Binds a local variable to the given value. If set from jstemplate
+ * jsvalue expressions, variable names must start with $, but in the
+ * API they only have to be valid javascript identifier.
+ *
+ * @param {string} name
+ *
+ * @param {Object?} value
+ */
+JsEvalContext.prototype.setVariable = function(name, value) {
+  this.vars_[name] = value;
+};
+
+
+/**
+ * Returns the value bound to the local variable of the given name, or
+ * undefined if it wasn't set. There is no way to distinguish a
+ * variable that wasn't set from a variable that was set to
+ * undefined. Used mostly for testing.
+ *
+ * @param {string} name
+ *
+ * @return {Object?} value
+ */
+JsEvalContext.prototype.getVariable = function(name) {
+  return this.vars_[name];
+};
+
+
+/**
+ * Evaluates a string expression within the scope of this context
+ * and returns the result.
+ *
+ * @param {string} expr A javascript expression
+ * @param {Element} opt_template An optional node to serve as "this"
+ *
+ * @return {Object?} value
+ */
+JsEvalContext.prototype.evalExpression = function(expr, opt_template) {
+  var exprFunction = jsEvalToFunction(expr);
+  return this.jsexec(exprFunction, opt_template);
+};
+
+
+/**
+ * Uninlined string literals for jsEvalToFunction() (IE6 perf).
+ */
+var STRING_a = 'a_';
+var STRING_b = 'b_';
+var STRING_with = 'with (a_) with (b_) return ';
+
+
+/**
+ * Cache for jsEvalToFunction results.
+ * @type Object
+ */
+JsEvalContext.evalToFunctionCache_ = {};
+
+
+/**
+ * Evaluates the given expression as the body of a function that takes
+ * vars and data as arguments. Since the resulting function depends
+ * only on expr, we cache the result so we save some Function
+ * invocations, and some object creations in IE6.
+ *
+ * @param {string} expr A javascript expression.
+ *
+ * @return {Function} A function that returns the value of expr in the
+ * context of vars and data.
+ */
+function jsEvalToFunction(expr) {
+  if (!JsEvalContext.evalToFunctionCache_[expr]) {
+    try {
+      // NOTE(mesch): The Function constructor is faster than eval().
+      JsEvalContext.evalToFunctionCache_[expr] =
+        new Function(STRING_a, STRING_b, STRING_with + expr);
+    } catch (e) {
+      log('jsEvalToFunction (' + expr + ') EXCEPTION ' + e);
+    }
+  }
+  return JsEvalContext.evalToFunctionCache_[expr];
+}
+
+
+/**
+ * Evaluates the given expression to itself. This is meant to pass
+ * through string attribute values.
+ *
+ * @param {string} expr
+ *
+ * @return {string}
+ */
+function jsEvalToSelf(expr) {
+  return expr;
+}
+
+
+/**
+ * Parses the value of the jsvalues attribute in jstemplates: splits
+ * it up into a map of labels and expressions, and creates functions
+ * from the expressions that are suitable for execution by
+ * JsEvalContext.jsexec(). All that is returned as a flattened array
+ * of pairs of a String and a Function.
+ *
+ * @param {string} expr
+ *
+ * @return {Array}
+ */
+function jsEvalToValues(expr) {
+  // TODO(mesch): It is insufficient to split the values by simply
+  // finding semi-colons, as the semi-colon may be part of a string
+  // constant or escaped.
+  var ret = [];
+  var values = expr.split(REGEXP_semicolon);
+  for (var i = 0, I = jsLength(values); i < I; ++i) {
+    var colon = values[i].indexOf(CHAR_colon);
+    if (colon < 0) {
+      continue;
+    }
+    var label = stringTrim(values[i].substr(0, colon));
+    var value = jsEvalToFunction(values[i].substr(colon + 1));
+    ret.push(label, value);
+  }
+  return ret;
+}
+
+
+/**
+ * Parses the value of the jseval attribute of jstemplates: splits it
+ * up into a list of expressions, and creates functions from the
+ * expressions that are suitable for execution by
+ * JsEvalContext.jsexec(). All that is returned as an Array of
+ * Function.
+ *
+ * @param {string} expr
+ *
+ * @return {Array.<Function>}
+ */
+function jsEvalToExpressions(expr) {
+  var ret = [];
+  var values = expr.split(REGEXP_semicolon);
+  for (var i = 0, I = jsLength(values); i < I; ++i) {
+    if (values[i]) {
+      var value = jsEvalToFunction(values[i]);
+      ret.push(value);
+    }
+  }
+  return ret;
+}