php isset() 等价于 javascript
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/5436953/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
php isset() equivalent in javascript
提问by ptamzz
I'm looking for the javascript equivalent of the php function isset(). I've tried the method described here at JavaScript isset() equivalentbut at firebug, error comes up saying
我正在寻找与 php 函数等效的 javascript isset()。我已经尝试了在JavaScript isset() 等效处描述的方法，但在萤火虫中，出现错误说
data.del is undefined //Firebug warning/error
if(typeof data.del[0].node != 'undefined') { // codes in my js file
And in some cases
而且在某些情况下
data is null //Firebug warning/error
if(typeof data.storyLine != 'undefined') { // codes in my js file
The logic seems to work but I'm wondering why is there an error then??
逻辑似乎有效，但我想知道为什么会出现错误？
Basically, I want to check whether data.del[0].nodeor data.storyLineisset or not??
基本上，我想检查是否data.del[0].node或data.storyLineisset与否？
采纳答案by zzzzBov
ECMAScript defines the hasOwnPropertymethod for checking if an object has a property of a given name:
ECMAScript 定义了hasOwnProperty检查对象是否具有给定名称的属性的方法：
var foo = {'bar':'bar'}
alert( foo.hasOwnProperty( 'bar' ) ); //true
alert( foo.hasOwnProperty( 'baz' ) ); //false
EDIT: This doesn't fully answer your question
编辑：这并不能完全回答你的问题
It's possible for a property to be set as undefined
可以将属性设置为 undefined
foo.bar = undefined;
alert( foo.hasOwnProperty( 'bar' ) ); //still true
The important question is: What do you need your truth table to be?
重要的问题是：你需要什么样的真值表？
In php:
在 php 中：
type | isset() | == true
------+---------+----------
null | false | false
false | true | false
true | true | true
"" | true | false
"a" | true | true
0 | true | false
1 | true | true
In JS:
在JS中：
type | isset() | truthy
----------+---------+--------
NaN | ? | false
undefined | ? | false
null | false | false
true | true | true
false | true | false
"" | true | false
"a" | true | true
0 | true | false
1 | true | true
回答by Bobby D
isset() makes two checks: first if the variable is defined, and second if it is null.
isset() 进行两项检查：第一次是否定义了变量，第二次是否为空。
You will have to check for both the 'undefined' case and the null case, for example:
您必须同时检查“未定义”情况和空情况，例如：
if (typeof data !== 'undefined' && data !== null)
回答by Harmen
I think the best solution is to look in the source code of php.js:
我认为最好的解决方案是查看php.js的源代码：
function isset () {
// !No description available for isset. @php.js developers: Please update the function summary text file.
//
// version: 1103.1210
// discuss at: http://phpjs.org/functions/isset
// + original by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
// + improved by: FremyCompany
// + improved by: Onno Marsman
// + improved by: Rafa? Kukawski
// * example 1: isset( undefined, true);
// * returns 1: false
// * example 2: isset( 'Kevin van Zonneveld' );
// * returns 2: true
var a = arguments,
l = a.length,
i = 0,
undef;
if (l === 0) {
throw new Error('Empty isset');
}
while (i !== l) {
if (a[i] === undef || a[i] === null) {
return false;
}
i++;
}
return true;
}
