为什么在触发事件之前调用事件句柄中的立即调用函数？

Question

let a = (function gigel() {    alert("dd");})(); * this is executed immediatly as the page loads*    <button onclick="a">Click me</button>* this is executed only when clicking the button *    <button onclick="alert('dd')">Click me</button> 

Answer 1

您正在调用事件(function gigel...)()，因为调用返回任何内容a都不是函数。也a没有被调用，你会想要以下内容：

let a = (function gigel() {

  alert("IIFE");

});

* this is executed immediately as the page loads*

<button onclick="a()">Click me</button> 

* this is executed only when clicking the button *

<button onclick="alert('dd')">Click me</button>

或者，如果您想立即调用它并将其存储在a：

let a = (function gigel() {

  alert("IIFE");

  return gigel;

})();

* this is executed immediately as the page loads*

<button onclick="a()">Click me</button> 

* this is executed only when clicking the button *

<button onclick="alert('dd')">Click me</button>