Question

I believe V8 underlying Node.js supports strict mode or ES5 by default.

Can we enable non strict or ECMASCRIPT 3 in V8 engine?

almost 100% of ES5 features are available in Chrome (V8) see compatibility table .

But some developers(including me) are still comfortable with ES3, can we have that option?

Answer 1

Just don’t include the string "use strict" in your code. V8 supports strict mode, it doesn’t use it unless you tell it to (i.e. it follows the ES5 specification).

Compare the following scripts:

Input:

foo = "Hello";
console.log(foo);

Output:

quentin@workstation:tmp # node test.js
Hello

and

Input:

"use strict";
foo = "Hello";
console.log(foo);

Output:

quentin@workstation:tmp # node test.js

node.js:201
        throw e; // process.nextTick error, or 'error' event on first tick
              ^
ReferenceError: foo is not defined
    at Object.<anonymous> (/Users/quentin/tmp/test.js:2:5)
    at Module._compile (module.js:432:26)
    at Object..js (module.js:450:10)
    at Module.load (module.js:351:31)
    at Function._load (module.js:310:12)
    at Array.0 (module.js:470:10)
    at EventEmitter._tickCallback (node.js:192:40)