length Property (Function) (JavaScript)

Gets the number of arguments defined for a function.




The required functionName is the name of the function.

The length property of a function is initialized by the scripting engine to the number of arguments in the function's definition when an instance of the function is created.

What happens when a function is called with a number of arguments different from the value of its length property depends on the function.


The following example illustrates the use of the length property:

function ArgTest(a, b){  
    var s = "";  

    s += "Expected Arguments: " + ArgTest.length;  
    s += "<br />";  
    s += "Passed Arguments: " + arguments.length;  

    return s;  

document.write(ArgTest(1, 2));  

// Output:   
// Expected Arguments: 2  
// Passed Arguments: 2  


Supported in the following document modes: Quirks, Internet Explorer 6 standards, Internet Explorer 7 standards, Internet Explorer 8 standards, Internet Explorer 9 standards, Internet Explorer 10 standards, Internet Explorer 11 standards. Also supported Store apps (Windows 8 and Windows Phone 8.1). See Version Information.

See Also

arguments Property (Function)
length Property (Array)
length Property (String)