Javascript: if (0 =='') condition is true (note the difference between == and ===)

A few days ago when writing javascript script code was found to determine if statements: if (v =='') when v is 0, the result was as true, such as:

<script type="text/javascript"
>
if(0 == '') {
 document.write(' I love fuck, eggs  <br/>');
}
if(0 == false) document.write('yes');
</script>

Implementation of results:
I speak, eggs pain
yes

Later if (0 == false) document.write ('yes'); is Ricki assume in dealing with different types of data == comparison, the first and then converted to a Boolean type to compare the test, but after I read the help of Javascript documents, found assumption is correct. Such as (the following excerpt from the documentation):

Equality operator (==,!=)
If the two different types of expression, is trying to convert them to strings, numbers, or Boolean quantity.
NaN and including itself does not equal any value.
Negative zero equals positive zero.
null and null and undefined are equal.
The same string, numerically equal to the number, the same object, the same Boolean value, or (when the type is not the same) can be forced into one of the above, are considered to be equal.
Other comparisons were considered not equal.

Identity operator (===,!==)
In addition to not to cast, and the type must be the same, these operators and the role of the equality operator is the same.

If the above change == === First, the results are:
yes

Free, welcome to the red sweet potato stroll

分类:Web 时间:2010-11-29 人气:128
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