callback学习笔记

let x = function(){
  console.log('xxxxx');
};
let y = function(callback){
  console.log('yyyyyy');
  // console.log(callback); // there var "callback" = x,because x inside
  callback(); // call the x function
};
y(x);

// Example 1 例题一和例题二对比学习.
//1.first edition;
let calc = function(num1, num2, calcType){
  if(calType === "add"){
    return num1 + num2;
  }else if(calType = "multiply"){
    return num1 * num2;
  };
};
console.log(calc(2,3,multiply))
//2. with callback
//add function there
let add = function(a, b){
  return a + b
};
//multiply
let multiply = function(a, b){
  return a * b
};
// the main function there
let calc = function(num1, num2, callback){
  return callback(num1, num2); //if callback it's add, then it's equal to return add(num1, num2)
};
console.log(calc(2,3,multiply))
// 2. with callback doWhatever
//add function there
let add = function(a, b){
  return a + b
};
//multiply
let multiply = function(a, b){
  return a * b
};
// dowhater passin as variable results
let doWhatever = function(a, b){
  //String interpolation:
  console.log('here are your two numbers back ${a}, ${b}');
};
// the main function there
let calc = function(num1, num2, callback){
  return callback(num1, num2); //if callback it's add, then it's equal to return add(num1, num2)
};
//!!!!!
console.log(cal(2,3, function(a, b) {
  return a -b;
}));
//The BAD SITUATION, callback must be a function name, if not, there will be wrong things happen, it the calc have to use "if condition";
let calc = function(num1, num2, callback){
  if(type of callback === function){
    return callback(num1, num2);
  }
}
// Example: 2
// The callback in sortfunction
var myArr = [{
  num: 5,
  str: 'apple'
},{
  num: 7, 
  str: 'ban'
}];
//we can change str to num, to get the sort results we want 
myArr.sort(function(val1, val2){
  if(val1.str > val2.str){
    return -1;
  }else {
    return 1;
  }
})
console.log(myArr);

// Example 3 
//选出大于5的内容with callback
var list = [5, 8, 9, 2, 7, 5];

function callback(list){
  var newList = [];
  
  for(var i =0; i<list.length; i++){
    if(list[i]>5){
      newList.push(list[i]);   
    }
    return newList;
  }
  function filter(list, callback){
    return callback(list);
  }
}

let filtered = filter(list, callback);
console.log(filtered);

学数据结构后看这些东西感觉特别简单... 觉得自己学早了前端...