javascript 中“has_key”的等价物是什么？
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What's the equivalent of "has_key" in javascript?
提问by TIMEX
if dictionary.has_key('school'):
How would you write this in javascript?
你会如何用javascript写这个？
回答by icktoofay
if(Object.prototype.hasOwnProperty.call(dictionary, key)) {
// ...
You can also use the inoperator, but sometimes it gives undesirable results:
您还可以使用的in运营商，但有时给人意想不到的结果：
console.log('watch' in dictionary); // always true
回答by kay - SE is evil
Either with the inoperator:
要么与in运营商：
if('school' in dictionary) { …
Or probably supported in more bowsers: hasOwnProperty
或者可能在更多的浏览器中得到支持： hasOwnProperty
if({}.hasOwnProperty.call(dictionary, 'school')) { …
Could be problematic in border cases: typeof
在边境情况下可能会出现问题： typeof
if(typeof(dictionary.school) !== 'undefined') { …
One must not use != undefinedas undefined is not a keyword:
不得使用!= undefinedundefined不是关键字：
if(dictionary.school != undefined) { …
if(dictionary.school != undefined) { …
But you can use != nullinstead, which is true for null, undefinedand absent values:
但是你可以使用!= null，而不是，这是真实的null，undefined并没有值：
if(dictionary.school != null) { …
回答by Peter
You may also try:
你也可以试试：
if(dictionary.hasOwnProperty('school'))
The hasOwnPropertymethod will only evaluate to trueif the property is actually on the instance, and not simply inherited from the prototype -- as is the case with in.
该hasOwnProperty方法只会评估true属性是否确实在实例上，而不是简单地从原型继承——就像in.
For instance, evaluting ('toString' in myObject)will be true, while myObject.hasOwnProperty('toString')will be false.
例如，评估('toString' in myObject)将是true，而myObject.hasOwnProperty('toString')将是false。
回答by swalk
The 'in' operator.
“输入”运算符。
if ('school' in dictionary)
回答by kennebec
Or even,
甚至，
if(dictionary.school!=undefined)
