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<style>.box {background-color: yellow;color: red;}.active {border: 1px solid #333;}.em {background-color: rgb(0, 238, 255);color: rgb(255, 0, 34);}.bgc {background-color: greenyellow;}</style></head><body><div class="box">php中文网</div><script>let box = document.querySelector(".box");console.log(box);//添加classbox.classList.add("active");//判断是否有classconsole.log(box.classList.contains("box"));//替换classbox.classList.replace("box", "em");//移除classbox.classList.remove("em");//toggle 有去无加box.classList.toggle("bgc");</script>
//焦点移除密码不能为空document.forms.login.password.onblur = function () {if (this.value.length === 0) {alert("密码不能为空");return false;}};
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