javascript substring method support for interger - chrome

Question

When I try to assign number value to JavaScript keyword name as like below

var a="12345";
var b=a.substring(1,3)
console.log(b);
var name=12345;
var y=name.substring(1,3)
console.log(y);

I excepted it to throw the type error, but it produces the same output for variable b and name.

I'm aware that keywords should not be used as variable, still curious to know how it works.

JS does not care about the type means not strongly typed, so when you write name.substring , js does not know if its a string,int or object. at run time its just parse it to string and do the function. the same is true when you try to add 1+"123", it wil lgive you 1123 not error — Atul, Aug 18 '18 at 12:18
That is why now a days people use typescript to avoid such scenarios. — Atul, Aug 18 '18 at 12:19
`name` is `window.name` which is always a string. @Atul you can't use substring on a Number-typed variable. Note that using `let` instead of `var` would allow you to redefine that variable. — Jeto, Aug 18 '18 at 12:20
@Jeto the question is why its not throwing an error, that what i was explaining. — Atul, Aug 18 '18 at 12:21
@Atul If you replace `name` with anything else in his 4th line you'll get an error. The reason it's not throwing one is because `var name = 12345` does not create an integer variable because it overwrites `window.name` which is a string (and has to be one). — Jeto, Aug 18 '18 at 12:22

score 3 · Accepted Answer · answered Aug 18 '18 at 12:30

name refers to window.name, a string (which looks to be enforced by browsers).

When you write var name = 12345; you basically overwrite it (due to how var works, see differences betwen var and let).

Since window.name must hold a string, it's therefore converted to '12345' internally.

1 Answers1