Question

each() method in jQuery contains such a statement:

callback.call( value, i, value ) 

I couldn’t understand what this statement means exactly.

I know what callback and call mean but I couldn’t get the arguments of the function call: (value,i,value). What does this mean?

The statement is used in a for block of each() but my question is independent of that context.

from the jQuery source:

for ( var value = object[0];
      i < length &&
      callback.call( value, i, value ) // <=== LOOK!
      !== false;
      value = object[++i] ) {}

Answer 1

The call method exists on all functions in Javascript. It allows you to call the function and in doing so set the value of this within that function.

function myFunc() {
    console.log(this);
}

myFunc.call(document.body);

In this example, this within myFunc will be document.body.

The first parameter of call is the value to be set as this; subsequent parameters are passed on to the function as normal parameters. So, in your example:

callback.call( value, i, value )

this is equivalent to

callback(i, value)

except that, within the callback, this is now also set to value.