Why directly updating charater at index does not work in javascript [duplicate]

Question

Can somebody explain this behaviour

Code:

name = "ABC"
console.log(name)

name[0] = "B"
console.log(name)

Output Expected:

ABC
BBC

Actual Output :

Not only that it doesn't work, if you are in a function with strict mode ("use strict;" as the first statement), it will throw an error, for example (in Chrome) TypeError: Cannot assign to read only property '0' of string 'ABC' — qrsngky
– qrsngky, Commented Sep 7, 2023 at 6:08
He asked for the reason why I think. Strings are immutable that is the reason why his code doesn't work — Ilja KO
– Ilja KO, Commented Sep 7, 2023 at 6:08
A quote from MDN: When using bracket notation for character access, attempting to delete or assign a value to these properties will not succeed. The properties involved are neither writable nor configurable. — qrsngky
– qrsngky, Commented Sep 7, 2023 at 6:12

Dramatic_Monk810 · Accepted Answer · 2023-09-07 06:50:59Z

5

Strings are immutable/readonly due to the fact that they are primitive data types in JavaScript. You can only generate new strings.

name = "ABC"
console.log(name)

name = "B" + name.slice(1);
console.log(name)

To read more about primitives-MDN-Primitives

Dramatic_Monk810

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answered Sep 7, 2023 at 6:05

Ilja KO

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Comments

Rasel · Accepted Answer · 2023-09-07 06:58:20Z

0

By creating a new string with the desired modification, you achieve the desired result while keeping the original name variable intact.

let name = "ABC";
console.log(name);

name = "B" + name.substring(1); // Concatenate "B" with the rest of the string
console.log(name);

answered Sep 7, 2023 at 6:58

Rasel

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