[英]What does in do or mean in an if statement?
I am JavaScript learner. 我是JavaScript学习者。 I like to skim code to learn new things.
我喜欢略读代码以学习新事物。 Recently i was looking in jQuery and found a condition like :
if ( "zoom" in div.style )
. 最近,我正在使用jQuery,发现了类似条件:
if ( "zoom" in div.style )
。 What is in
and whats the condition being tested for here? 什么是
in
和什么条件正在这里进行测试?
It tests for the existence of a property in an object (including prototyped properties). 它测试对象中属性的存在(包括原型属性)。
Example: http://jsfiddle.net/6RVD2/1/ 示例: http : //jsfiddle.net/6RVD2/1/
var obj = {someProp: 'someValue',
anotherProp: 'anotherValue'
};
var empty_obj = {};
function F() {};
F.prototype.someProp = 'someValue';
var proto_obj = new F;
if( 'someProp' in obj ) {
alert('yep'); // alert fires
}
if( 'someProp' in empty_obj ) {
alert('yep'); // alert doesn't fire
}
if( 'someProp' in proto_obj ) {
alert('yep'); // alert fires
}
See the in
operator . 参见
in
运算符 。
It checks whether the object div.style
as the property zoom
(ie div.style.zoom
). 它检查对象
div.style
是否作为属性 zoom
(即div.style.zoom
)。
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