Javascript 立即调用函数模式

Question

你怎么称呼这些模式？它们之间有什么区别？你什么时候使用它们？还有其他类似的模式吗？

(function() {
    console.log(this);  // window
})();

(function x() {
    console.log(this);  // window
})();

var y = (function() {
    console.log(this);  // window
})();

var z = function() {
    console.log(this);  // window
}();

编辑:我刚刚发现了另外两种看似多余的方法，通过在最后两种情况下命名函数...

var a = (function foo() {
    console.log(this);  // window
})();

var b = function bar() {
    console.log(this);
}();

EDIT2:这是@GraceShao 在下面提供的另一种模式，它使函数可以在函数范围之外访问。

(x = function () {
    console.log(this);  // window
    console.log(x);     // function x() {}
})();
console.log(x);         // function x() {}

// I played with this as well 
// by naming the inside function 
// and got the following:

(foo = function bar() {
    console.log(this);  // window
    console.log(foo);   // function bar() {}
    console.log(bar);   // function bar() {}
})();
console.log(foo);       // function bar() {}
console.log(bar);       // undefined

Answer 1

这里再次是您的函数，并附有一些说明它们何时/为何有用的注释:

(function() {
    // Create a new scope to avoid exposing 
    // variables that don't need to be
    // This function is executed once immediately
})();

(function fact(i) {
    // This named immediately invoked function 
    // is a nice way to start off recursion
    return i <= 1 ? 1 : i*fact(i - 1);
})(10);

var y = (function() {
    // Same as the first one, but the return value 
    // of this function is assigned to y
    return "y's value";
})();

var z = function() {
    /* This is the exact same thing as above 
     (except it is assigned to z instead of y, of course).
     The parenthesis in the above example don't do anything
     since this is already an expression
    */
}();