HarmonyOS string类型的字符串截取

export function substringByByte(str: string, start: number, end?: number): string { 
  const bytes = new Uint8Array([...str].map(c => c.charCodeAt(0))); 
  const slicedBytes = bytes.slice(start, end); 
  return String.fromCharCode(...slicedBytes); 
} 
// xx.ets 
const str = 'hello 世界'; 
console.log('substringByByte info:'+substringByByte(str, 0, 5)); // 输出 "hello" 
 
2：Uint8Array和string相互转换的方法 
stringToUint8Array(str: string): Uint8Array { 
  try { 
    let textEncoder = new util.TextEncoder(); 
    let array: Uint8Array = textEncoder.encodeInto(str); 
    return array 
  } catch (err) { 
    return new Uint8Array() 
  } 
} 
 
uint8ArrayToString(arr: Uint8Array): string { 
  let str = '' 
  if (arr && arr.length > 0) { 
    try { 
      let textDecode = util.TextDecoder.create('utf-8') 
      str = textDecode.decodeWithStream(arr) 
    } catch (err) { 
    } 
  } 
  return str 
}