JavaScript string matching only at the start versus using indexOf?

Question

I currently am matching user input as follows:

user_input = "upload a file"

if ( "upload a file".indexOf(user_input.toLowerCase()) > -1 ) {}

This work fine but the problem is, it matches "a file" which I don't want. I want it to only match if the beginning is correct.

This should match:

"upload"
"u"
"upload a"

This should not match, because the string does not match from the start:

"a"
"file"

Are there any suggestions on how to make this happen with indexOf?

Compare the return value of indexOf to zero: stackoverflow.com/questions/1767246/… — Vikdor
– Vikdor, Commented Sep 18, 2012 at 17:37
Vikdor, that doesn't work because indexOf matches anywhere in the string, which I don't want. I don't wnat anywhere in the string only from the start. — Sarahpre
– Sarahpre, Commented Sep 18, 2012 at 17:38
@Sarahpre Vikdor's point is that if it does match at the start of the string the result will be zero — Alnitak
– Alnitak, Commented Sep 18, 2012 at 17:40

Musa · Accepted Answer · 2012-09-18 17:39:13Z

4

indexOf return the index of the match, so if you want to test if it match at the beginning just check if it returns 0

user_input = "upload a file"
if ( "upload a file".indexOf(user_input.toLowerCase()) == 0 ) {}

answered Sep 18, 2012 at 17:39

Musa

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1 Comment

For the sake of JS sanity, that should probably be ===. :-)

Micah · Accepted Answer · 2012-09-18 17:42:47Z

1

<script>
user_input = "upload a file"
if ( "upload a file".**substr**(0, user_input.length) == user_input.toLowerCase()) {}
</script>

Use the inputs to your advantage...

Grab first X characters of the string, and make sure the whole string matches or any number of the characters you would like.

answered Sep 18, 2012 at 17:42

Micah

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Michal Klouda · Accepted Answer · 2012-09-18 17:38:25Z

0

What you describe means you want compare with zero:

if ( "upload a file".indexOf(user_input.toLowerCase()) == 0) { }

answered Sep 18, 2012 at 17:38

Michal Klouda

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