你认为每个程序员都应该知道JavaScript的哪些“隐藏特性”?
在看到以下问题的优质答案后,我认为是时候向JavaScript请求它了。
HTML的隐藏特性 CSS的隐藏特性 PHP的隐藏特性 ASP的隐藏特性。网 c#的隐藏特性 Java的隐藏特性 Python的隐藏特性
尽管JavaScript可以说是目前最重要的客户端语言(问问谷歌就知道了),但令人惊讶的是,大多数web开发人员很少意识到它的强大。
你认为每个程序员都应该知道JavaScript的哪些“隐藏特性”?
在看到以下问题的优质答案后,我认为是时候向JavaScript请求它了。
HTML的隐藏特性 CSS的隐藏特性 PHP的隐藏特性 ASP的隐藏特性。网 c#的隐藏特性 Java的隐藏特性 Python的隐藏特性
尽管JavaScript可以说是目前最重要的客户端语言(问问谷歌就知道了),但令人惊讶的是,大多数web开发人员很少意识到它的强大。
当前回答
window.name的值在页面更改时保持不变,如果在同一个域中(如果在iframe中,使用document),可以被父窗口读取。getElementById(“你的帧的ID”). contentwindow .name来访问它),并且只受可用内存的限制。
其他回答
JavaScript中最快的循环是while(i——)循环。在所有浏览器中。 所以如果循环元素的处理顺序不是那么重要,你应该使用while(i——)形式:
var names = new Array(1024), i = names.length;
while(i--)
names[i] = "John" + i;
此外,如果你必须继续使用for()循环,请记住始终缓存.length属性:
var birds = new Array(1024);
for(var i = 0, j = birds.length; i < j; i++)
birds[i].fly();
要连接大字符串使用数组(它更快):
var largeString = new Array(1024), i = largeString.length;
while(i--) {
// It's faster than for() loop with largeString.push(), obviously :)
largeString[i] = i.toString(16);
}
largeString = largeString.join("");
它比循环中的largeString += "something"快得多。
下面是一些有趣的事情:
Comparing NaN with anything (even NaN) is always false, that includes ==, < and >. NaN Stands for Not a Number but if you ask for the type it actually returns a number. Array.sort can take a comparator function and is called by a quicksort-like driver (depends on implementation). Regular expression "constants" can maintain state, like the last thing they matched. Some versions of JavaScript allow you to access $0, $1, $2 members on a regex. null is unlike anything else. It is neither an object, a boolean, a number, a string, nor undefined. It's a bit like an "alternate" undefined. (Note: typeof null == "object") In the outermost context, this yields the otherwise unnameable [Global] object. Declaring a variable with var, instead of just relying on automatic declaration of the variable gives the runtime a real chance of optimizing access to that variable The with construct will destroy such optimzations Variable names can contain Unicode characters. JavaScript regular expressions are not actually regular. They are based on Perl's regexs, and it is possible to construct expressions with lookaheads that take a very, very long time to evaluate. Blocks can be labeled and used as the targets of break. Loops can be labeled and used as the target of continue. Arrays are not sparse. Setting the 1000th element of an otherwise empty array should fill it with undefined. (depends on implementation) if (new Boolean(false)) {...} will execute the {...} block Javascript's regular expression engine's are implementation specific: e.g. it is possible to write "non-portable" regular expressions.
[更新了一点,以回应良好的评论;请参阅评论]
“JavaScript中的扩展方法”通过prototype属性。
Array.prototype.contains = function(value) {
for (var i = 0; i < this.length; i++) {
if (this[i] == value) return true;
}
return false;
}
这将为所有Array对象添加一个contains方法。您可以使用以下语法调用此方法
var stringArray = ["foo", "bar", "foobar"];
stringArray.contains("foobar");
如果你盲目地eval()一个JSON字符串来反序列化它,你可能会遇到问题:
这并不安全。该字符串可能包含恶意函数调用! 如果你没有将JSON字符串括在括号中,属性名可能会被误认为是标签,导致意外的行为或语法错误: Eval ("{\"foo\": 42}");//语法错误:无效标签 Eval ("({\"foo\": 42})");/ /好吧
未定义就是未定义。所以你可以这样做:
if (obj.field === undefined) /* ... */