Javascript 无法从classname js菜单中读取值，表示无法读取属性classname var mainNav=document.getElementsByClassName（“js菜单”）； var navBarToggle=document.getElementById（“js navbar切换”）； addEventListener（“单击”，函数（）{ 控制台日志（mainNav）； 对于（var i=0；i`enter code here`

Shara，您正在使用，请先阅读如何提问（），然后重新表述您的问题，以便其他人可以帮助您。可能重复

var mainNav = document.getElementsByClassName("js-menu");
var navBarToggle = document.getElementById("js-navbar-toggle");

navBarToggle.addEventListener("click", function() {
   console.log(mainNav);
      for (var i = 0; i `enter code here`<= mainNav.length; i++) {
    console.log(mainNav[i]);
    mainNav[i].classList.toggle("responsive");
  }
});

var mainNav = document.getElementsByClassName("js-menu");
var navBarToggle = document.getElementById("js-navbar-toggle");

navBarToggle.addEventListener("click", function() {
   console.log(mainNav);
      for (var i = 0; i < mainNav.length; i++) {
    console.log(mainNav[i]);
    mainNav[i].classList.toggle("responsive");
  }
});

var mainNav = document.getElementsByClassName("js-menu");
var navBarToggle = document.getElementById("js-navbar-toggle");

navBarToggle.addEventListener("click", function() {
   console.log(mainNav);
      for (var i = 0; i <= mainNav.length - 1 ; i++) {
    console.log(mainNav[i]);
    mainNav[i].classList.toggle("responsive");
  }
});