Hopefully the title is self explanatory, what is the advantage of using the .call() method in Javascript compared with just writing functionName(); ?
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There is also functionName.apply(). See 15.5.4.3 and 15.5.4.4 in ecma-international.org/publications/files/ECMA-ST/Ecma-262.pdfsome– some2009-01-21 17:37:04 +00:00Commented Jan 21, 2009 at 17:37
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3 Answers
functionName.call() takes an object instance as its first parameter. It then runs functionName within the context of that object instance (ie "this" is the specified instance)
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If you don't pass anything into call(), it will be the same; the function will be run with the same scope that the call to call() is made:
function test() {
alert(this);
}
test(); // alerts the window object
test.call(); // alerts the window object
But if you pass an object into call(), that object will be used as the scope:
test.call("hi"); // alerts "hi"
Comments
Let me show an example:
<html>
<head>
<script type="text/javascript">
var developerName = "window";
function test(){
var developer = function(developerName ){ this.developerName = developerName;}
developer.prototype = {
displayName : function(){alert(this.developerName );}
}
var developerA = new developer("developerA");
var developerB = new developer("developerB");
developerA.displayName();//will display an alert box with "developerA" as its inner text
developerA.displayName.call();//will display an alert box with "window" as its inner text, in this case the context is the window object.
developerA.displayName.call(developerB);//will display an alert box with "developerB" as its inner text
}
</script>
</head>
<body>
<input type="button" onclick="test()" value="display names"/>
<body>
</html>
Further reading:
http://www.alistapart.com/articles/getoutbindingsituations
Hope this helps.
