Find first match chinese and insert some text before it

Demo.js

function insertBeforeFirstChinese(string, insertedString) {
    
    // cf. https://stackoverflow.com/questions/21109011/javascript-unicode-string-chinese-character-but-no-punctuation
    const index = string.split("")
        .findIndex(char => /\p{Script=Han}/u.test(char))
        
    if (index > 0) {
      string = string.substr(0, index) + insertedString + string.substr(index);
    }
    
    return string
}

let source  = "中文 english"
let source1 = "english 中文"
let source2 = "english"
let source3 = "eng 中文 lish"


console.log(insertBeforeFirstChinese(source, 'aaa'))
console.log(insertBeforeFirstChinese(source1, 'aaa'))
console.log(insertBeforeFirstChinese(source2, 'aaa'))
console.log(insertBeforeFirstChinese(source3, 'aaa'))