ES5 Compliance for ServiceNow

ServiceNow runs on Mozilla Rhino engine which only supports ES5 JavaScript (2009 standard). All server-side scripts MUST use ES5 syntax.

Forbidden Syntax (WILL CAUSE SyntaxError)

ES6+ Syntax ES5 Alternative

const x = 5

var x = 5

let items = []

var items = []

() => {}

function() {}

Hello ${name}

'Hello ' + name

for (x of arr)

for (var i = 0; i < arr.length; i++)

{a, b} = obj

var a = obj.a; var b = obj.b;

[a, b] = arr

var a = arr[0]; var b = arr[1];

...spread

Use Array.prototype.slice.call()

class MyClass {}

Use constructor functions

async/await

Use GlideRecord callbacks

Promise

Use GlideRecord with callbacks

Common Patterns

Variable Declarations

// WRONG - ES6 const MAX_RETRIES = 3 let currentUser = gs.getUser()

// CORRECT - ES5 var MAX_RETRIES = 3 var currentUser = gs.getUser()

Functions

// WRONG - Arrow functions var active = incidents.filter((inc) => inc.active) var process = () => { return "done" }

// CORRECT - ES5 functions var active = [] for (var i = 0; i < incidents.length; i++) { if (incidents[i].active) { active.push(incidents[i]) } } var process = function () { return "done" }

String Concatenation

// WRONG - Template literals var message = Incident ${number} assigned to ${user}

// CORRECT - String concatenation var message = "Incident " + number + " assigned to " + user

Loops

// WRONG - for...of for (var item of items) { gs.info(item) }

// CORRECT - Traditional for loop for (var i = 0; i < items.length; i++) { gs.info(items[i]) }

Default Parameters

// WRONG - Default parameters function process(incident, priority = 3) { // ... }

// CORRECT - Manual defaults function process(incident, priority) { if (typeof priority === "undefined") { priority = 3 } // ... }

Automatic Validation

Before deploying any server-side script:

• Check for const /let declarations - convert to var

• Check for arrow functions =>

• convert to function()

• Check for template literals `

• convert to string concatenation

• Check for destructuring {a, b}

• convert to explicit property access

• Check for for...of loops - convert to index-based loops

Exception: Client Scripts

Client-side scripts (Client Scripts, UI Policies) run in the browser and MAY support ES6+ depending on user's browser. However, for maximum compatibility, ES5 is still recommended.