动态执行 JS

eval

特点：同步，当前作用域

var a = 1
function exec(code) {
  var a = 2
  eval(code)
}
exec('console.log("a",a)')
console.log('sync')

setTimeout

特点：异步，全局作用域

var a = 1
function exec(code) {
  var a = 2
  setTimeout(code, 0)
}

exec('console.log("a",a)')
console.log('sync')

创建 script 元素

特点：同步，全局作用域

var a = 1
function exec(code) {
  var a = 2
  const script = document.createElement('script')
  script.innerHTML = code
  document.body.appendChild(script)
}

exec('console.log("a",a)')
console.log('sync')

Function

特点：同步，全局作用域

var a = 1
function exec(code) {
  var a = 2
  const fn = new Function(code)
  fn()
}

exec('console.log("a",a)')
console.log('sync')