Polyfills

Ready-to-use polyfill implementations for the 20 missing or broken Array and String methods in SFMC SSJS.

Copy the polyfills you need to the top of your SSJS script block (before any usage). Add only the ones you actually use — each one adds a small amount of overhead.

Usage Pattern

<script runat="server">
// 1. Add polyfills at the very top (before any code that uses them)
Array.prototype.forEach = Array.prototype.forEach || function(callback) {
    for (var i = 0; i < this.length; i++) {
        callback(this[i], i, this);
    }
};

// 2. Now use the polyfilled methods normally
var emails = [];
rows.forEach(function(row) {
    emails.push(row["Email"]);
});
</script>

The || function(...) guard prevents re-defining methods that may become available in future engine updates.

Important: Some array method names (indexOf, lastIndexOf) are ambiguous with String.prototype methods of the same name. The polyfills below only add to Array.prototype — String.prototype.indexOf works correctly without polyfilling.

---

Array Polyfills

forEach

Array.prototype.forEach = Array.prototype.forEach || function(callback) {
    if (typeof callback !== 'function') { return; }
    for (var i = 0; i < this.length; i++) {
        callback(this[i], i, this);
    }
};

map

Array.prototype.map = Array.prototype.map || function(callback) {
    if (typeof callback !== 'function') { return []; }
    var result = [];
    for (var i = 0; i < this.length; i++) {
        result.push(callback(this[i], i, this));
    }
    return result;
};

filter

Array.prototype.filter = Array.prototype.filter || function(predicate) {
    if (typeof predicate !== 'function') { return []; }
    var result = [];
    for (var i = 0; i < this.length; i++) {
        if (predicate(this[i], i, this)) { result.push(this[i]); }
    }
    return result;
};

find

Array.prototype.find = Array.prototype.find || function(predicate) {
    if (typeof predicate !== 'function') { return undefined; }
    for (var i = 0; i < this.length; i++) {
        if (predicate(this[i], i, this)) { return this[i]; }
    }
    return undefined;
};

findIndex

Array.prototype.findIndex = Array.prototype.findIndex || function(predicate) {
    if (typeof predicate !== 'function') { return -1; }
    for (var i = 0; i < this.length; i++) {
        if (predicate(this[i], i, this)) { return i; }
    }
    return -1;
};

indexOf (Array)

Note: String.prototype.indexOf already works. This only polyfills Array.prototype.indexOf.

Array.prototype.indexOf = Array.prototype.indexOf || function(searchValue, fromIndex) {
    var start = fromIndex || 0;
    for (var i = start; i < this.length; i++) {
        if (this[i] === searchValue) { return i; }
    }
    return -1;
};

lastIndexOf (Array — broken, must override)

Array.prototype.lastIndexOf exists but always returns -1. Override it unconditionally:

Array.prototype.lastIndexOf = function(searchValue, fromIndex) {
    var start = (fromIndex !== undefined) ? fromIndex : this.length - 1;
    for (var i = start; i >= 0; i--) {
        if (this[i] === searchValue) { return i; }
    }
    return -1;
};

includes

Array.prototype.includes = Array.prototype.includes || function(searchValue) {
    for (var i = 0; i < this.length; i++) {
        if (this[i] === searchValue) { return true; }
    }
    return false;
};

some

Array.prototype.some = Array.prototype.some || function(predicate) {
    if (typeof predicate !== 'function') { return false; }
    for (var i = 0; i < this.length; i++) {
        if (predicate(this[i], i, this)) { return true; }
    }
    return false;
};

every

Array.prototype.every = Array.prototype.every || function(predicate) {
    if (typeof predicate !== 'function') { return true; }
    for (var i = 0; i < this.length; i++) {
        if (!predicate(this[i], i, this)) { return false; }
    }
    return true;
};

reduce

Array.prototype.reduce = Array.prototype.reduce || function(callback, initialValue) {
    if (typeof callback !== 'function') { return initialValue; }
    var accumulator = (arguments.length > 1) ? initialValue : this[0];
    var startIndex  = (arguments.length > 1) ? 0 : 1;
    for (var i = startIndex; i < this.length; i++) {
        accumulator = callback(accumulator, this[i], i, this);
    }
    return accumulator;
};

reduceRight

Array.prototype.reduceRight = Array.prototype.reduceRight || function(callback, initialValue) {
    if (typeof callback !== 'function') { return initialValue; }
    var accumulator = (arguments.length > 1) ? initialValue : this[this.length - 1];
    var startIndex  = (arguments.length > 1) ? this.length - 1 : this.length - 2;
    for (var i = startIndex; i >= 0; i--) {
        accumulator = callback(accumulator, this[i], i, this);
    }
    return accumulator;
};

fill

Array.prototype.fill = Array.prototype.fill || function(value, startIndex, endIndex) {
    var start = startIndex || 0;
    var end = (!endIndex || endIndex > this.length) ? this.length : endIndex;
    for (var i = start; i < end; i++) {
        this[i] = value;
    }
    return this;
};

splice (broken — must override)

Array.prototype.splice exists but ignores its first two arguments. Override unconditionally:

Array.prototype.splice = function(startIndex, deleteCount) {
    var arr = this;
    var endIndex = startIndex + deleteCount;
    var before = [];
    var removed = [];
    var after = [];
    for (var i = 0; i < arr.length; i++) {
        if (i < startIndex)      { before.push(arr[i]); }
        else if (i < endIndex)   { removed.push(arr[i]); }
        else                     { after.push(arr[i]); }
    }
    for (var j = 2; j < arguments.length; j++) {
        before.push(arguments[j]);
    }
    var merged = before.concat(after);
    var maxLen = arr.length > merged.length ? arr.length : merged.length;
    for (var k = 0; k < maxLen; k++) {
        if (k < merged.length) { arr[k] = merged[k]; }
        else                   { arr.pop(); }
    }
    return removed;
};

Array.isArray (static)

Array.isArray = Array.isArray || function(value) {
    return Object.prototype.toString.call(value) === '[object Array]';
};

Array.of (static)

Array.of = Array.of || function() {
    var result = [];
    for (var i = 0; i < arguments.length; i++) {
        result.push(arguments[i]);
    }
    return result;
};

---

String Polyfills

trim

String.prototype.trim = String.prototype.trim || function() {
    return this.replace(/^[\s\uFEFF\xA0]+|[\s\uFEFF\xA0]+$/g, '');
};

startsWith

String.prototype.startsWith = String.prototype.startsWith || function(searchString, position) {
    position = position || 0;
    return this.indexOf(searchString, position) === position;
};

endsWith

String.prototype.endsWith = String.prototype.endsWith || function(search, length) {
    var len = (length === undefined || length > this.length) ? this.length : length;
    return this.substring(len - search.length, len) === search;
};

---

Complete Polyfill Bundle

If you want all polyfills at once, paste this block at the top of your script:

// SFMC SSJS Polyfill Bundle — add only what you need
Array.prototype.forEach   = Array.prototype.forEach   || function(cb) { if (typeof cb!=='function') return; for (var i=0;i<this.length;i++) cb(this[i],i,this); };
Array.prototype.map       = Array.prototype.map       || function(cb) { if (typeof cb!=='function') return []; var r=[]; for (var i=0;i<this.length;i++) r.push(cb(this[i],i,this)); return r; };
Array.prototype.filter    = Array.prototype.filter    || function(cb) { if (typeof cb!=='function') return []; var r=[]; for (var i=0;i<this.length;i++) if (cb(this[i],i,this)) r.push(this[i]); return r; };
Array.prototype.find      = Array.prototype.find      || function(cb) { if (typeof cb!=='function') return; for (var i=0;i<this.length;i++) if (cb(this[i],i,this)) return this[i]; };
Array.prototype.findIndex = Array.prototype.findIndex || function(cb) { if (typeof cb!=='function') return -1; for (var i=0;i<this.length;i++) if (cb(this[i],i,this)) return i; return -1; };
Array.prototype.indexOf   = Array.prototype.indexOf   || function(v,f) { for (var i=f||0;i<this.length;i++) if (this[i]===v) return i; return -1; };
Array.prototype.includes  = Array.prototype.includes  || function(v) { for (var i=0;i<this.length;i++) if (this[i]===v) return true; return false; };
Array.prototype.some      = Array.prototype.some      || function(cb) { if (typeof cb!=='function') return false; for (var i=0;i<this.length;i++) if (cb(this[i],i,this)) return true; return false; };
Array.prototype.every     = Array.prototype.every     || function(cb) { if (typeof cb!=='function') return true; for (var i=0;i<this.length;i++) if (!cb(this[i],i,this)) return false; return true; };
Array.prototype.lastIndexOf = function(v,f) { var s=(f!==undefined)?f:this.length-1; for (var i=s;i>=0;i--) if (this[i]===v) return i; return -1; }; // broken native — always override
String.prototype.trim     = String.prototype.trim     || function() { return this.replace(/^[\s\uFEFF\xA0]+|[\s\uFEFF\xA0]+$/g,''); };
String.prototype.startsWith = String.prototype.startsWith || function(s,p) { p=p||0; return this.indexOf(s,p)===p; };
String.prototype.endsWith   = String.prototype.endsWith   || function(s,l) { var n=(l===undefined||l>this.length)?this.length:l; return this.substring(n-s.length,n)===s; };
Array.isArray = Array.isArray || function(v) { return Object.prototype.toString.call(v)==='[object Array]'; };