富在酒吧 - “在'操作的JavaScript？ [英] foo in bar - 'in' operator javascript?

问题描述

我最近看了关于CSS的浏览器功能检测的教程......最终产品是这样的事情...

I recently read a tutorial on CSS browser feature detection... The end product was something like this...

var prefix = ['Moz', 'webkit', 'O', 'ms', 'Khtml'],
    test_style = document.createElement('div').style;

var css_check = function(prop) {
    if (prop in test_style) {
        return true;
    }
    for (var i = 0; i < prefix.length; i++) {
        if (prefix[i] + prop in test_style) {
            return true;
        }
    }
    return false;
};

css_check('whatev_css_property');

我不明白的部分是这个...

The part I dont understand is this...

如果（在test_style道具）或如果（巴富）。

从我读过如果（巴富）用来检查一个值是一个数组，但我可能是错在这里，我没有发现这么多的文档。此外，如果这是在使用一个数组来检查值是如何为 test_style =使用document.createElement（'DIV'）。风格数组？无厘头...

From what I've read if (foo in bar) is used to check if a value is in an array but I might be wrong here, I haven't found much documentation on this. Also, if this is used to check values in an array HOW is test_style = document.createElement('div').style an array? Doesn't make sense...

我是可怕的困惑。任何澄清将大大AP preciated。

I am terrible confused. Any clarification would be greatly appreciated.

推荐答案

的在运算符用于检查一个的键的presence 的在数组或对象，如：

The in operator is used to check for the presence of a key in an array or object, e.g.

3 in [1, 2, 3] // false, since the array indices only go up to 2
2 in [1, 2, 3] // true
'x' in { x: 5 } // true
'toString' in Object.prototype // true

的风格属性存在的的CSSStyleDeclaration ，其中包含在活动的浏览器支持的每个样式属性的属性。

The style property there is an instance of CSSStyleDeclaration, which contains properties for each supported style attribute in the active browser.

在code片段在您检查后给观看浏览器是否支持这种风格的一些版本（无论是官方的一个或与多家供应商共同prefixes之一）。

The code snippet you gave in your post checks whether the viewing browser supports some version of that style (either the official one or with one of a number of common vendor prefixes).

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