Function Methods

Function prototype methods in SSJS — call and apply work natively (ES3), while bind is unavailable because Function.prototype is sealed.

Function.prototype.call and Function.prototype.apply are ES3 and work natively in SSJS — both are value-confirmed on a CloudPage. Function.prototype.bind (ES5) is not available, and unlike Array.prototype / String.prototype, Function.prototype is sealed, so bind cannot be installed on the prototype — use a standalone helper instead. Each section heading is tagged with its ECMAScript edition.

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call (ES3)

Calls the function with a given this value and arguments supplied individually.

fn.call(thisArg[, arg1[, arg2[, ...]]])

Parameters

Name	Type	Description
thisArg	any	The value to use as this when calling the function
arg1, arg2, …	any	Arguments passed to the function (optional, repeatable)

Return Value

any — whatever the called function returns.

Example

function greet(greeting) {
    return greeting + ", " + this.name;
}
var r = greet.call({ name: "Sam" }, "Hi");
Write(r);  // Hi, Sam

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apply (ES3)

Calls the function with a given this value and arguments supplied as an array.

fn.apply(thisArg[, argsArray])

Parameters

Name	Type	Description
thisArg	any	The value to use as this when calling the function
argsArray	Array	Array of arguments to pass to the function (optional)

Return Value

any — whatever the called function returns.

Example

function sum(a, b) {
    return a + b;
}
var r = sum.apply(null, [2, 3]);
Write(r);  // 5

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bind (unavailable — use the bindFn helper) (ES5)

Function.prototype.bind is not available in SSJS, and Function.prototype is sealed — assigning Function.prototype.bind = … silently has no effect. Use the standalone bindFn helper from Polyfills instead.

bindFn(fn, thisArg[, ...preArgs]) returns a new function with this and any leading arguments pre-bound (it is built on the native apply):

function bindFn(fn, thisArg) {
    var preArgs = [];
    for (var i = 2; i < arguments.length; i++) { preArgs.push(arguments[i]); }
    return function () {
        var callArgs = [];
        for (var a = 0; a < preArgs.length; a++) { callArgs.push(preArgs[a]); }
        for (var b = 0; b < arguments.length; b++) { callArgs.push(arguments[b]); }
        return fn.apply(thisArg, callArgs);
    };
}

var greet = function (greeting, name) { return greeting + ", " + name + "!"; };
var sayHi = bindFn(greet, null, "Hi");
Write(sayHi("Ada"));  // Hi, Ada!