Strict
To keep the old code working, modern modifications are off by default.
/**
* Modern modifications are off by default,
* to keep the old code working
*
* When 'use script' it is located at the top of a script,
* the whole script works the “modern” way
* starting with ECMAScript 5
* .
*/
"use strict";
let a = 1; // Correct
b = 1; // ReferenceError: b is not defined
Classes
Modern JavaScript supports classes and modules (use strict enabled by default).
/**
* In classes and modules, strict is enabled by default
*/
try {
class MyClass {
constructor() {
a = 1; // Look Here
}
}
new MyClass();
} catch (err) {
console.log(err.message); // a is not defined
}
Last update: 210 days ago
