弱类型语言javascript开发中的一些坑实例小结【变

test1();
function test1() {
  function setName() {
    name = '张三'; // 此处没有var声明，提升至全局
  }
  setName();
  console.log(name);// '张三'
}

test2();
function test2() {
  var a = 1;
  function haha() {
    console.log(a);
    var a=1;
  }
  haha(); // undefined
}

test3();
function test3() {
  var b=2;
  function hehe(){
    window.b = 3; // 此时的b为全局变量的b
    console.log(b); // 此时的b是函数test3()里的b为2
  }
  hehe();
}

test4();
function test4() {
  c = 5;
  function heihei() {
    var c;
    window.c = 3;
    console.log(c); // 函数heihei内的c为undefined
    console.log(window.c); // 3
  }
  heihei();
}

test5();
function test5() {
  var arr = [];
  arr[0] = '1';
  arr[1] = 'b';
  arr[9] = 100;
  console.log(arr.length); // 10
}

test6();
function test6() {
  var a = 1;
  console.log(a++); // 1
  console.log(++a); // 3
  console.log(null == undefined); // true
  console.log(null === undefined);// false
  console.log(1 == "1"); // true
  console.log(1 === "1"); // false
  console.log(NaN === NaN) // false;
}

test7();
function test7() {
  console.log(typeof 1); // number
  console.log(typeof "hello"); // string
  console.log(typeof typeof "hello"); // string
  console.log(typeof !!"hello"); // boolean
  console.log(typeof /[0-9]/); // object
  console.log(typeof {}); // object
  console.log(typeof null); // object
  console.log(typeof undefined); // undefined
  console.log(typeof [1, 2, 3]); // object
  console.log(toString.call([1, 2, 3])); // [object Array]
  console.log(typeof function () {}); // function
}

test8();
function test8() {
  console.log(parseInt(3.14));// 3
  console.log(parseFloat('3.01aaa'));// 3.01
  console.log(parseInt('aa1.2'));// NaN;
  console.log(parseInt('8.00',16));// 8
  console.log(parseInt('0x8',16));// 8
  console.log(parseInt('8.00',10));// 8
  console.log(parseInt('010',8));// 10
  console.log(parseInt('1000',2));// 1000
}

test9();
function test9() {
  function bar() {
    return foo;
    foo = 10;
    function foo(){};
  }
  console.log(typeof bar()); // 'function'
}

test10();
function test10() {
  var foo = 1;
  function bar() {
    foo = 10;
    console.log(typeof foo);
    return;
    function foo(){};
  }
  bar(); // number
  console.log(foo); // 1
}

test11();
function test11() {
  console.log(typeof a); // function
  var a = 3;
  function a(){};
  console.log(typeof a); // number
}

test12();
function test12() {
  function foo(a) {
    console.log(a);// 1
    arguments[0] = 2;
    console.log(a);// 2
    console.log(arguments.length);// 3
  }
  foo(1,3,4);
}

test13();
function test13() {
  var foo = function bar(name) {
    console.log("hello " + name);
  }
  foo("world");
  console.log(bar); // 此处会报错 bar is not defined
}

test14();
function test14() {
  function foo() {
    console.log('I am foo');
  }
  console.log('正常执行');
  setTimeout((function(){
    console.log('定时器大灰狼来啦');
  }),0);
  foo();
}