只执行一次的js 函数。

function runOnce(fn, context) { //控制让函数只触发一次
    return function () {
        try {
            fn.apply(context || this, arguments);
        }
        catch (e) {
            console.error(e);//一般可以注释掉这行
        }
        finally {
            fn = null;
        }
    }
}

// Usage 1:
var a = 0;
var canOnlyFireOnce = runOnce(function () {
    a++;
    console.log(a);
});

canOnlyFireOnce(); //1
canOnlyFireOnce(); // nothing
canOnlyFireOnce(); // nothing

// Usage 2:
var name = "张三";
var canOnlyFireOnce = runOnce(function () {
    console.log("你好" + this.name);
});
canOnlyFireOnce(); //你好张三
canOnlyFireOnce(); // nothing

// Usage 3:
var obj = {name: "天涯孤雁", age: 24};
var canOnlyFireOnce = runOnce(function () {
    console.log("你好" + this.name);
}, obj);
canOnlyFireOnce(); //你好天
canOnlyFireOnce(); // nothing

因为返回函数执行一次后，fn = null将其设置未null，所以后面就不会执行了。

方法2：

function once(fn, context) {
    var result;

    return function() {
        if(fn) {
            result = fn.apply(context || this, arguments);
            fn = null;
        }

        return result;
    };
}

// Usage
var canOnlyFireOnce = once(function() {
    console.log(‘Fired!‘);
});

canOnlyFireOnce(); // "Fired!"
canOnlyFireOnce(); // nothing