Missing & Broken Methods

Array and String prototype methods that are unavailable or return wrong results in SFMC SSJS, with manual workarounds.

The SFMC SSJS engine is missing many Array and String methods that are available in modern JavaScript. Some methods exist on the prototype but return incorrect results (marked as “broken”). All can be replaced with polyfills — see the Polyfills page.

Missing Array Methods

These methods do not exist in SFMC SSJS and will throw an error if called:

Method	Workaround
Array.prototype.forEach	for loop
Array.prototype.map	Manual for loop building a new array
Array.prototype.filter	Manual for loop with condition
Array.prototype.find	Manual for loop, return on match
Array.prototype.findIndex	Manual for loop returning index
Array.prototype.indexOf	Manual for loop comparing values
Array.prototype.includes	Manual for loop
Array.prototype.some	Manual for loop with early return true
Array.prototype.every	Manual for loop with early return false
Array.prototype.reduce	Manual for loop with accumulator
Array.prototype.reduceRight	Reverse for loop with accumulator
Array.prototype.fill	Manual for loop assigning value
Array.prototype.copyWithin	Manual for loop
Array.prototype.entries	Manual index-based iteration
Array.isArray	Object.prototype.toString.call(v) === "[object Array]"
Array.of	Array literal or [].concat(args)

Broken Array Methods

These methods exist in SSJS but return incorrect results:

Array.prototype.splice — broken

splice ignores its startIndex and deleteCount arguments — it behaves as if both are 0, effectively inserting all elements at the beginning.

var arr = [1, 2, 3, 4, 5];
arr.splice(2, 1);
// Expected: [1, 2, 4, 5]  (remove element at index 2)
// Actual:   [1, 2, 3, 4, 5]  (nothing removed — start/count ignored!)

Use the polyfill from the Polyfills page.

Array.prototype.lastIndexOf — broken

lastIndexOf always returns -1, regardless of the input:

var arr = [1, 2, 3, 2, 1];
arr.lastIndexOf(2);
// Expected: 3
// Actual:   -1  (always!)

Use the polyfill from the Polyfills page.

Missing String Methods

Method	Workaround
String.prototype.trim	str.replace(/^\s+\|\s+$/g, "")
String.prototype.startsWith	str.indexOf(sub) === 0
String.prototype.endsWith	str.slice(-sub.length) === sub

Note: String.prototype.indexOf is available and works correctly for strings. The indexOf missing-method warning only applies to Array.prototype.indexOf.

Safe Array Methods (Available in SSJS)

These work correctly without polyfills:

Method	Notes
Array.prototype.push	Add to end
Array.prototype.pop	Remove from end
Array.prototype.shift	Remove from front
Array.prototype.unshift	Add to front
Array.prototype.slice	Non-mutating sub-array
Array.prototype.join	Join to string
Array.prototype.sort	In-place sort (lexicographic by default)
Array.prototype.reverse	In-place reverse
Array.prototype.concat	Merge arrays
Array.prototype.length	Length property

Manual Equivalents (Without Polyfills)

// forEach equivalent
for (var i = 0, len = arr.length; i < len; i++) {
    process(arr[i]);
}

// map equivalent
var result = [];
for (var i = 0, len = arr.length; i < len; i++) {
    result.push(transform(arr[i]));
}

// filter equivalent
var filtered = [];
for (var i = 0, len = arr.length; i < len; i++) {
    if (predicate(arr[i])) { filtered.push(arr[i]); }
}

// find equivalent
var found = null;
for (var i = 0, len = arr.length; i < len; i++) {
    if (predicate(arr[i])) { found = arr[i]; break; }
}

// indexOf equivalent
function indexOfValue(arr, value) {
    for (var i = 0; i < arr.length; i++) {
        if (arr[i] === value) { return i; }
    }
    return -1;
}

// includes equivalent
function includesValue(arr, value) {
    for (var i = 0; i < arr.length; i++) {
        if (arr[i] === value) { return true; }
    }
    return false;
}

// Array.isArray equivalent
function isArray(value) {
    return Object.prototype.toString.call(value) === "[object Array]";
}

→ For ready-to-use polyfill implementations, see Polyfills