SOURCE

function keywordFlag(word, flag) {
  let result = word
  if (word && typeof word && flag) {
    if (!Array.isArray(flag)) {
      result = result.replace(new RegExp(flag, 'g'), function(w) {
        return `<span class="wordflag">${w}</span>`
      })
    } else {
      let arr = [...new Set(flag)]
      arr.forEach((item) => {
        result = result.replace(new RegExp(item, 'g'), function(w) {
          return `<span class="wordflag">${w}</span>`
        })
      })
    }
  }
  return result
}

let str= '测试数据中的一个是智子制造的假象'
let str2= '测试数据中的一个是智子制造的假象'
let arr= ['测试','智子','一个','假象']
let arr2= NaN

 let item = document.getElementById('item');
 let item2 = document.getElementById('item2');
    //    设置HTML
    item.innerHTML = keywordFlag( str , arr)
    item2.innerHTML = keywordFlag( str2 , arr2)

<p id="item">
<p/>
<br/>
<p id="item2">
<p/>
<br/>

.wordflag{
    color: red
}
#item{
    font-size: 22px
}
#item2{
    font-size: 22px
}