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Vitaliy Terziev
Vitaliy Terziev

Reputation: 6701

JS wrapper objects strange behaviour

Can someone explain the behaviour below, it is about the temporary wrapper objects in JS, but when I try to use them on number literal they fail. Am I mistaken or this changed recently, I tried on V8 and Gecko, same story.

    'stringWrapper'.charAt(0);
    "s"
    1.toString();
    VM8363:2 Uncaught SyntaxError: Unexpected token ILLEGAL(…)InjectedScript._evaluateOn @ VM8253:875InjectedScript._evaluateAndWrap @ VM8253:808InjectedScript.evaluate @ VM8253:664
    typeof 1
    "number"
    (1+0).toString();
    "1"
    typeof (1+0)
    "number"

Upvotes: 1

Views: 92

Answers (2)

Jay
Jay

Reputation: 1056

More interesting JavaScript things: 1 .toString() is valid! 1. toString() is not.

You may enjoy Kyle Simpson's video on weird JavaScript quirks

Upvotes: 0

Henrik Andersson
Henrik Andersson

Reputation: 47222

This is an interesting "feature" in JavaScript and other dynamically typed languages, like Python, where you can call methods or access properties on an integer.

What's actually happening is that the engine sees, or lexes, the 1.toString() as a floating point number where the toString() part is where the first decimal should be.

The solution is either to double-dot it, 1..toString() and omit the trailing decimal or wrap the number within parenthesis (1).toString() to evaluate the number and then call toString on the result.

Upvotes: 3

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