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    Function

    Summary

    Every function in JavaScript is actually a Function object.

    Syntax

    new Function ([arg1[, arg2[, ...argN]],] functionBody)

    Parameters

    arg1, arg2, ... argN
    Names to be used by the function as formal argument names. Each must be a string that corresponds to a valid JavaScript identifier or a list of such strings separated with a comma; for example "x", "theValue", or "a,b".
    functionBody
    A string containing the JavaScript statements comprising the function definition.

    Description

    Function objects created with the Function constructor are parsed when the function is created. This is less efficient than declaring a function and calling it within your code, because functions declared with the function statement are parsed with the rest of the code.

    All arguments passed to the function are treated as the names of the identifiers of the parameters in the function to be created, in the order in which they are passed.

    Note: Functions created with the Function constructor do not create closures to their creation contexts; they always are created in the global scope. When running them, they will only be able to access their own local variables and global ones, not the ones from the scope in which the Function constructor was called. This is different from using eval  with code for a function expression. 

    Invoking the Function constructor as a function (without using the new operator) has the same effect as invoking it as a constructor.

    Example

    Creating functions with the Function constructor is one of the ways to dynamically create an indeterminate number of new objects with some executable code into the global scope from a function. The following example (a recursive shortcut to massively modify the DOM) is impossible without the invocation of the Function constructor for each new query if you want to avoid closures.

    <!doctype html>
    <html>
    <head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
    <title>MDN Example - a recursive shortcut to massively modify the DOM</title>
    <script type="text/javascript">
    var domQuery = (function() {
      var aDOMFunc = [
            Element.prototype.removeAttribute,
            Element.prototype.setAttribute,
            CSSStyleDeclaration.prototype.removeProperty,
            CSSStyleDeclaration.prototype.setProperty
          ];
    
      function setSomething (bStyle, sProp, sVal) {
        var  bSet = Boolean(sVal), fAction = aDOMFunc[bSet | bStyle << 1],
             aArgs = Array.prototype.slice.call(arguments, 1, bSet ? 3 : 2),
             aNodeList = bStyle ? this.cssNodes : this.nodes;
    
        if (bSet && bStyle) { aArgs.push(""); }
        for (
          var nItem = 0, nLen = this.nodes.length;
          nItem < nLen;
          fAction.apply(aNodeList[nItem++], aArgs)
        );
        this.follow = setSomething.caller;
        return this;
      }
    
      function setStyles (sProp, sVal) { return setSomething.call(this, true, sProp, sVal); }
      function setAttribs (sProp, sVal) { return setSomething.call(this, false, sProp, sVal); }
      function getSelectors () { return this.selectors; };
      function getNodes () { return this.nodes; };
    
      return (function (sSelectors) {
        var oQuery = new Function("return arguments.callee.follow.apply(arguments.callee, arguments);");
        oQuery.selectors = sSelectors;
        oQuery.nodes = document.querySelectorAll(sSelectors);
        oQuery.cssNodes = Array.prototype.map.call(oQuery.nodes, function (oInlineCSS) { return oInlineCSS.style; });
        oQuery.attributes = setAttribs;
        oQuery.inlineStyle = setStyles;
        oQuery.follow = getNodes;
        oQuery.toString = getSelectors;
        oQuery.valueOf = getNodes;
        return oQuery;
      });
    })();
    </script>
    </head>
    
    <body>
    
    <div class="testClass">Lorem ipsum</div>
    <p>Some text</p>
    <div class="testClass">dolor sit amet</div>
    
    <script type="text/javascript">
      domQuery(".testClass").attributes("lang", "en")("title", "Risus abundat in ore stultorum")
      .inlineStyle("background-color", "black")("color", "white")("width", "100px")("height", "50px");
    </script>
    </body>
    
    </html>
    

    Properties

    For properties available on Function instances, see Properties of Function instances.

    The global Function object has no specific properties of its own, however, like all function objects it has a length, prototype and name property.

    Properties inherited from Function:

    Methods

    For methods available on Function instances, see Methods of Function instances.

    The global Function object has no methods of its own, however, since it is a function itself it does inherit some methods through the prototype chain from Function.prototype.

    Methods inherited from Function:

    Function instances

    Function instances inherit from Function.prototype. As with all constructors, you can change the constructor's prototype object to make changes to all Function instances.

    Properties

    Function.arguments
    An array corresponding to the arguments passed to a function. This is deprecated as property of Function, use the arguments object available within the function instead.
    Function.arity
    Used to specifiy the number of arguments expected by the function, but has been removed. Use the length property instead.
    Function.caller
    Specifies the function that invoked the currently executing function.
    Function.length
    Specifies the number of arguments expected by the function.
    Function.name
    The name of the function.
    Function.displayName
    The display name of the function.
    Function.prototype.constructor
    Specifies the function that creates an object's prototype. See Object.constructor for more details.
    Properties inherited from Object:

    Methods

    Function.prototype.apply()
    Applies the method of another object in the context of a different object (the calling object); arguments can be passed as an Array object.
    Function.prototype.bind()
    Creates a new function which, when called, itself calls this function in the context of the provided value, with a given sequence of arguments preceding any provided when the new function was called.
    Function.prototype.call()
    Calls (executes) a method of another object in the context of a different object (the calling object); arguments can be passed as they are.
    Function.prototype.isGenerator()
    Returns true if the function is a generator; otherwise returns false.
    Function.prototype.toSource()
    Returns a string representing the source code of the function. Overrides the Object.toSource method.
    Function.prototype.toString()
    Returns a string representing the source code of the function. Overrides the Object.toString method.

    Example: Specifying arguments with the Function constructor

    The following code creates a Function object that takes two arguments.

    // Example can be run directly in your JavaScript console
    
    // Create a function that takes two arguments and returns the sum of those arguments
    var adder = new Function("a", "b", "return a + b");
    
    // Call the function
    adder(2, 6);
    // > 8

    The arguments "a" and "b" are formal argument names that are used in the function body, "return a + b".

    Browser compatibility

    Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
    Basic support (Yes) (Yes) ? ? ?
    Feature Android Firefox Mobile (Gecko) IE Phone Opera Mobile Safari Mobile
    Basic support ? (Yes) ? ? ?

    See also

    Document Tags and Contributors

    Contributors to this page: Bergi, teoli
    最近更新: teoli,