autofocus HTML5
This Boolean attribute lets you specify that a form control should have input focus when the page loads, unless the user overrides it, for example by typing in a different control. Only one form element in a document can have the autofocus attribute, which is a Boolean. It cannot be applied if the type attribute is set to hidden (that is, you cannot automatically set focus to a hidden control).

给输入框加上这个属性就行了
mdn链接

另外不明白为什么 element.focus()会没有用。不贴出代码无法解决，随手写了一下测试是有用的

trigger，模拟点击