Unexpected behavior adding stringified integer to decimal in js

Question

I had a strange bug that I just found the source of in my code.

"1" + .88 // 10.88

What's going on here?

Denys Séguret · Accepted Answer · 2016-01-04 15:04:13Z

8

When adding a number and a string (whatever their order), the number is converted to a string and then the two are concatenated.

.88.toString()

is

"0.88"

So you get the string

"10.88"

which appears as

10.88

in most contexts (for example in an HTML input).

If you want a specification based analysis, it starts here with

Then the number to string conversion with the leading 0.is described here: (s=88, k=2, n=0)

answered Jan 4, 2016 at 14:39

Denys Séguret

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3 Comments

but why 1 is converted to 10 in his case?

@JurijJazdanov It's not, the 0 is coming from .88.

@NinaScholz It's the same for the addition: when one of the operands is a string, the other is converted to a string, whatever the order.