recursive

  • The function calls itself
  • The function goes to the exit, gets the value, and then goes up one step at a time to get the final result
  • Performance is poor because you are waiting for a value
  • N factorial
function fn1(a) {
  if (a === 1) return 1;
  return a * fn1(a-1);
}

console.log(fn1(5));
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  • Implement the Fibonacci sequence
//	1 1 2 3 5 8 13
function fn2(n){
  if(n === 1 || n === 2)  return 1;
  return fn2(n - 2) + fn2(n - 1);
}

console.log(fn2(5));
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precompiled

  • Js execution process
    • Check for syntax errors
    • precompiled
    • Explain a line, execute a line
  • Imply Global variables
    • A global variable that is assigned a value without being declared
b = 2; 	// window.b === 2;
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  • Precompile time functions declare overall promotion, variables only declare promotion, not assignment.
var a = 2; // 1. Declare a variable 2.2 to a.
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  • Precompile the solution
    • Code, whether executed or not, generates a variable boost during precompilation. For example:if(){}The statement in, even if the condition is not met, produces a variable promotion
    • Precompile in function
      • AO (Activation Object active object function context)
        1. Look for parameters and variable declarations in functions
        2. The argument value is assigned to the parameter
        3. Find the declaration of the function body, and assign the function body
        4. Executive function
      • Problem sets
function test(a){
   console.log(a);   
   var a = 1;
   console.log(a);   
   function  a(){};
   console.log(a);  
   var b =function (){};
   console.log(b);  
   function  d(){};
 }
 test(2);
 
 // AO = {
 // a : undefined -> 2 -> function(){... } - > 1
 // b : undefined -> function(){... }
 // d : function(){... }
 / /}
        
    // function a(){... }, 1, 1, function b(){... }
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function test(a, b){
   console.log(a); 
   c = 0;
   var c;
   a = 5;
   b = 6;
   console.log(b); 
   function b(){};
   function d(){};
   console.log(b); 
 }
test(1);

// AO = {
// a : undefined -> 1 -> 5;
// b : undefined -> function b(){... } - > 6;
// c : undefined -> 0;
// d : function d(){... }
// }
     
//  1,6,6
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  • GO Global Context (Window)
    1. Looking for a variable
    2. Find a function declaration
    3. perform
    • Problem sets
 console.log(a, b);
 function a(){}
 var b = function (){}

 // GO = {
 // b: undefined -> function (){}
 // a: function a(){... }
 // }

 // function a(){... } undefined
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var b = 3;
console.log(a);
function a (a){
console.log(a);
var a = 2;
console.log(a);
function a (){}
var b = 5;
console.log(b);
}
a(1);
// GO = {
// b: 3
//  a: function a(){....}
// }
// AO ={
// a: undefined -> function a(){... } - > 2,
// b: 5
// }

// function a(){.... }, function a(){... }, 2, 5
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 a = 1;
 function test(){
   console.log(a);
   a = 2;
   console.log(a);
   var a = 3;
   console.log(a);
 }

 test();
 var a;

// GO = {
// a : undefined ,
// test : function test(){... }
// }
// AO = {
// a : undefined, 2, 3
// }

// undefined, 2, 3
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  function test(){
   console.log(b);
   if(a){
     var b = 2;
   }
   c = 3;
   console.log(c);
 }

var a;
test();
a = 1;
console.log(a);

// GO = {
// a : undefined
// test: function(){... },
// c : 3
// }
// AO = {
// b : undefined
// }

// undefined, 3 ，1
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function test(){
  return a;
  a = 1;
  function a(){}
  var a = 2;
}

console.log(test());
// AO = {
//  a: function a(){...}
// }

// function a(){... }
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function test(){
  a = 1;
  function a (){}
  var a = 2;
  return a;
}

console.log(test());

// AO = {
//  a: function a(){...}, 1, 2
// }

/ / 2
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a = 1; function test(e){ function e(){} arguments[0] = 2; console.log(e); if(a){ var b = 3; } var c; a = 4; var a; console.log(b); f = 5; console.log(c); console.log(a); } var a; test(1); // G0 = { // a: 1, // test: function test(e){... } // f: 5 // } // AO = { // e: undefined -> 1 -> function e(){... } -> 2, // b: undefined, // c: undefined, // a: undefined -> 4, // // } // 2, undefined, undefined, 4Copy the code