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
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]
其他回答
你可以使用for in迭代数组
Mark Cidade指出了for in循环的用处:
// creating an object (the short way, to use it like a hashmap)
var diner = {
"fruit":"apple"
"veggetable"="bean"
}
// looping over its properties
for (meal_name in diner ) {
document.write(meal_name+"<br \n>");
}
结果:
fruit
veggetable
但还有更多。因为你可以使用关联数组这样的对象,你可以处理键和值, 就像foreach循环一样:
// looping over its properties and values
for (meal_name in diner ) {
document.write(meal_name+" : "+diner[meal_name]+"<br \n>");
}
结果:
fruit : apple
veggetable : bean
因为数组也是对象,你可以用同样的方法迭代其他数组:
var my_array = ['a', 'b', 'c'];
for (index in my_array ) {
document.write(index+" : "+my_array[index]+"<br \n>");
}
结果:
0 : a
1 : b
3 : c
可以很容易地从数组中删除一个已知元素
var arr = ['a', 'b', 'c', 'd'];
var pos = arr.indexOf('c');
pos > -1 && arr.splice( pos, 1 );
你可以很容易地打乱一个数组
arr.sort(function() Math.random() - 0.5);-不是真正的随机分布,见评论。
Function.toString()(隐性):
function x() {
alert("Hello World");
}
eval ("x = " + (x + "").replace(
'Hello World',
'STACK OVERFLOW BWAHAHA"); x("'));
x();
Javascript中的所有对象都实现为哈希表,因此它们的属性可以通过索引器访问,反之亦然。此外,你可以使用for/in操作符枚举所有属性:
var x = {a: 0};
x["a"]; //returns 0
x["b"] = 1;
x.b; //returns 1
for (p in x) document.write(p+";"); //writes "a;b;"
私有方法
对象可以有私有方法。
function Person(firstName, lastName) {
this.firstName = firstName;
this.lastName = lastName;
// A private method only visible from within this constructor
function calcFullName() {
return firstName + " " + lastName;
}
// A public method available to everyone
this.sayHello = function () {
alert(calcFullName());
}
}
//Usage:
var person1 = new Person("Bob", "Loblaw");
person1.sayHello();
// This fails since the method is not visible from this scope
alert(person1.calcFullName());
函数在JavaScript中是第一类公民:
var passFunAndApply = function (fn,x,y,z) { return fn(x,y,z); };
var sum = function(x,y,z) {
return x+y+z;
};
alert( passFunAndApply(sum,3,4,5) ); // 12
函数式编程技术可以用来编写优雅的javascript。
特别是,函数可以作为参数传递,例如Array.filter()接受回调:
[1, 2, -1].filter(function(element, index, array) { return element > 0 });
// -> [1,2]
你也可以声明一个“private”函数,它只存在于特定函数的作用域中:
function PrintName() {
var privateFunction = function() { return "Steve"; };
return privateFunction();
}