This is the code
let name = 'John';
name[1] = 'a';
name[2] = 'n';
name[3] = 'e';
I know Javascript strings are immutable. The lines 2, 3 and 4 are not gonna work and if I console.log(name), the output will be 'John'. But why is Js not throwing an error for line 2, 3, 4 ?
In sloppy mode, certain types of failures are frequently silent. In this case, the index properties of the string are non-writable:
console.log(
Object.getOwnPropertyDescriptor('foo', 1)
);And assigning to a non-writable property will:
Specifically, this logic is implemented in PutValue.
If succeeded is false and V.[[Strict]] is true, throw a TypeError exception.
If you want to make these sorts of silent bugs into explicit errors, use strict mode:
'use strict';
let name = 'John';
name[1] = 'a';