SOURCE

function sayHello(){
  let hello = document.getElementById('hello')
  this.content = "Hello JSRun, My name is zhanzhan.wei！please take care"
  typing(hello,this.content)
}


function typing(dom,content,bool){
  console.log
  this.content = content
  this.i = 0
  
  this.typing = function(){
    if(this.i<this.content.length+1){
      dom.innerHTML = this.content.slice(0,this.i++)+'_'
      setTimeout(()=>{
         this.typing()
      },200)
    }else{
       dom.innerHTML = this.content
       if(!bool)sayName()
    }
   
  }
  this.typing()
}
sayHello()

<div>
  <h1 id="hello"></h1>
  <h2 id="name"></h2>
</div>