I came across some javascript code I don't understand:
what does a < 5 mean if the variable a holds a string?
Thanks
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ECMA Specs for JavaScript comparison bclary.com/2004/11/07/#a-11.9.3RHT– RHT2011-10-24 23:44:06 +00:00Commented Oct 24, 2011 at 23:44
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3 Answers
If a holds the string representation of a number, JavaScript will implicitly convert it to a number and perform the comparison.
Otherwise, it will return false.
For example:
var a = 'foo';
(a < 5) // will be false
(a > 5) // will be false
a = '10';
(a < 5) // will be false
(a > 5) // will be true
3 Comments
RHT
If a is null or undefined and other variations , refer ECMA Specs for JavaScript comparison bclary.com/2004/11/07/#a-11.9.3
Christian C. Salvadó
Even if the string doesn't represent a number, it will be converted to Number, e.g. in your
var a = 'foo' snippet, the string 'foo' gets converted to NaN, and if one of the operands is NaN false is always the result.
Same as if it held a number, due to JavaScript's (occasionally twisted) type conversion rules.
That said, code that relies on that always makes me a little twitchy; IMO it should be converted to a number manually so it can be sanity-checked under more-controlled conditions.
Comments
var a = '5';
a < 5; // false
a > 5; // false
a == 5; // true
a === 5; // false <-- pay attention
var a = 5;
a < 5; // false
a > 5; // false
a == 5; // true
a === 5; // true <-- pay attention
var a = 'anythingelse';
a < 5; // false
a > 5; // false
a == 5; // false
a === 5; // false
