意外的严格模式保留字“让”

Question

我收到此错误：

  

意外的严格模式保留字

当我尝试运行此代码时：

"use strict";
var
fs = require('fs'),
spawn = require('child_process').spawn,
filename = process.argv[2];

if(!filename){
  throw Error('A File to watch must be specified!');
}
fs.watch(filename,function(){
    let ls = spawn('ls',['-lh',filename]);
    ls.stdout.pipe(process.stdout);
});
console.log("now watching " + filename + " for changes.....");