JSON.stringify() function

JSON.stringify

var  obj = {a: 1, b:2}
console.log(JSON.stringify(obj)) // {"a":1,"b":1}

var obj1 = {
  a:1,
  b: function() {
    console.log(1)
  },
  c: undefined
}
// 不会输出c,b
console.log(JSON.stringify(obj1)) // {"a":1} 

//JSON.stringify(value [, replacer [, space]])  
/*
  replacer 接受一个函数，每个属性都会过滤一变
  space 格式化
*/

var replacer = function (k, v) {
  if (v == undefined) {
    return 'undefined'
  }
  if (typeof v === 'function') {
    return Function.prototype.toString.call(v)
  }
  return v
}
var obj1 = {
  a:1,
  b: function() {
    console.log(1)
  },
  c: undefined
}
console.log(JSON.stringify(obj1,replacer)) // {"a":1,"b":"function () {\n    console.log(1)\n  }","c":"undefined"}