如何在第一页加载时执行JavaScript函数？ [英] How can I execute a JavaScript function on the first page load?

问题描述

我想知道是否有一种方法只在第一次页面加载时执行一次JavaScript函数，然后在任何后续重新加载时都不执行。

I am wondering if there is a way to execute a JavaScript function once only on the first ever page load and then not execute on any subsequent reloads.

是否存在我可以这样做吗？

Is there a way I can go about doing this?

推荐答案

以下代码将在 onload 事件触发。该声明检查 如果 一次性函数之前已经执行 NOT ，则使用标志（ hasCodeRunBefore ），然后存储在 localStorage的 。

The code below will execute once the onload event fires. The statement checks if the onetime function has NOT been executed before by making use of a flag (hasCodeRunBefore), which is then stored in localStorage.

window.onload = function () {
    if (localStorage.getItem("hasCodeRunBefore") === null) {
        /** Your code here. **/
        localStorage.setItem("hasCodeRunBefore", true);
    }
}

注意：如果用户清除浏览器的 localStorage 无论如何，该函数将再次运行，因为标志（ hasCodeRunBefore ）将被删除。

Note: If the user clears their browsers' localStorage by any means, then the function will run again because the flag (hasCodeRunBefore) will have been removed.

使用 localStorage 因为操作员和长卷功能而会很乏味名。我创建了一个基本的模块来简化这个，所以上面的代码将替换为：

Using localStorage can be tedious because of operators and long winded function names. I created a basic module to simplify this, so the above code would be replaced with:

window.onload = function () {
    if (!ls.exists('has_code_run_before')) {
        /** Your code here... **/
        ls.set.single('has_code_run_before', true);

        /** or... you can use a callback. **/
        ls.set.single('has_code_run_before', true, function () {
           /** Your code here... **/ 
        });
    }
};

更新＃1

Per @PatrickRoberts评论，您可以使用 在 运算符中查看localStorage中是否存在变量键，所以

Update #1

Per @PatrickRoberts comment, you can use the in operator to see if a variable key exists in localStorage, so

if (localStorage.getItem('hasCodeRunBefore') === null)

成为

if (!('hasCodeRunBefore' in localStorage))

并且更简洁，更清洁。

其次，您可以设置像对象一样的值（ localStorage.hasCodeRunBefore = true ）虽然它将被存储为字符串，而不是布尔值（或者您的值是什么数据类型）。

Secondly, you can set values as you would an object (localStorage.hasCodeRunBefore = true) though it will be stored as a string, not as boolean (or whatever data type your value is).

这篇关于如何在第一页加载时执行JavaScript函数？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！