CODEWITHSUNDEEP
javascript
Jared Roberts
Jared Roberts

Reputation: 153

Why is this JavaScript interpreted two different ways?

Can someone please explain why this JavaScript is interpreted two different ways?

This:

var testnum = $("<div>00000001</div>").text();
var test = "claimid:" + + testnum;
alert(test);

This throws an alert that displays: claimid:1

Where this:

var testnum = $("<div>00000001</div>").text();
var test = "claimid:" + testnum;
alert(test);

This throws an alert that displays: claimid:00000001

I get the reason as to why the second treats testnum as a string, but why does it treat testnum as a number on the first.

Upvotes: 1

Views: 70

Answers (3)

000
000

Reputation: 27247

In the first case, + is interpreted as the unary positive operator. Consider x = -5. The - is the unary negative operator. + takes a value and returns its numeric value.

Upvotes: 1

Adam Rackis
Adam Rackis

Reputation: 83366

but why does it treat testnum as a number on the first.

Remember, in JavaScript, + can be used as a unary operator to convert a string to a number. That's what you have here with the second plus sign:

var test = "claimid:" + + testnum;
//                      ^ HERE

In either case, the string concatenation takes higher precedence than numeric addition (where applicable), but the first case converts your value of 00000001 to a number, which is why a plain old 1 is displayed.

Upvotes: 1

Paul
Paul

Reputation: 141907

You have two plus signs. The second plus sign is the unary plus operator, which in Javascript has the sole purpose of converting it's operand to a Number.

Upvotes: 4

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