Variables

Declaration

SSJS uses only var for variable declarations. let and const are not supported and will cause a runtime error.

var name = "Jane";
var count = 42;
var active = true;
var data = null;
var nothing; // undefined

Scope

Variables declared with var have function scope, not block scope. A variable declared inside an if block or for loop is accessible outside that block.

if (true) {
    var x = 10; // function-scoped, not block-scoped
}
Write(x); // 10 — works fine

for (var i = 0; i < 3; i++) {
    // ...
}
Write(i); // 3 — i is still accessible here

In SSJS, the “global scope” within a single <script runat="server"> block is the top-level scope. Variables declared at the top level of any script block are shared across all script blocks on the same page.

Hoisting

Function declarations are hoisted to the top of their containing scope. Variable declarations (not their values) are also hoisted.

// Function declarations are fully hoisted
greet(); // Works — even called before declaration

function greet() {
    Write("Hello!");
}

// Variable declarations are hoisted, but not their values
Write(y); // undefined (not an error, just undefined)
var y = 5;
Write(y); // 5

Hoisting across script blocks is NOT guaranteed. Always place function declarations in the first script block on a page.

Naming Conventions

SSJS follows standard JavaScript naming conventions. The SFMC community style guide recommends:

camelCase for local variables: subscriberKey, emailAddress, rowCount
PascalCase is reserved for platform objects: Platform, DataExtension, WSProxy
Prefix private/internal functions with _: _formatDate, _validateEmail
Constants (by convention only, no const): var MAX_ROWS = 200; (uppercase + underscores)

var subscriberKey = Platform.Request.GetQueryStringParameter("sk");
var emailAddress  = "";
var rowCount      = 0;

var MAX_RETRIES = 3;

function _formatName(first, last) {
    return first + " " + last;
}

Multiple Variables

Declare multiple variables with separate var statements (one per variable is most readable and lint-friendly):

// Preferred: one var per line
var first  = "Jane";
var last   = "Smith";
var email  = "jane@example.com";

// Also valid: comma-separated (harder to diff)
var a = 1, b = 2, c = 3;

Common Pitfalls

Forgetting var creates a global:

function doSomething() {
    result = "oops"; // ⚠️ No var — creates/overwrites global
}

Always use var inside functions to keep scope contained.

Variable leaking across iterations:

for (var i = 0; i < rows.length; i++) {
    var rowData = processRow(rows[i]); // rowData is re-declared each iteration
    // This works in SSJS but wouldn't in strict block-scoped languages
}
// rowData and i still accessible here