JavaScript Learning Experience 04

• Any value (including the Nan itself) is compared to Nan and returns false:

1 > NaN // false1 <= NaN // false‘1’ > NaN // false‘1’ <= NaN // falseNaN > NaN // falseNaN <= NaN // false

• When the array is compared with something else, it becomes a string and a person.
• When a non-array object is compared to something else, it becomes the string directly:
  ‘[object Object]’
• If two values are not of the same type, the strict equality operator === returns directly false , whereas the equality operator == converts them to the same type, and then compares them with the strict equality operator;
• NaNis not equal to any value (including itself). Also, positive 0 equals minus 0:

NaN === NaN  // false+0 === -0 // true

• When comparing data for two composite types (objects, arrays, functions), instead of comparing their values for equality, compare whether they point to the same address:

{} === {} // false[] === [] // false(function () {} === function () {}) // false

• undefinedand null strictly equal to oneself;
• Andnull == undefined // true
• Two variables that only declare unassigned are equal:

var v1;var v2;v1 === v2 // true

• Bitwise operators only work on integers, and if an operator is not an integer, it is automatically converted to an integer and then executed;
• Although inside JavaScript, values are stored as 64-bit floating-point numbers, but when you do bit operations, they are evaluated as 32-bit signed integers, and the return value is also a 32-bit signed integer:

function toInt32(x) {//将任意数值转化为32位整数  return x | 0;}

• The binary or operation of a decimal with 0 is equivalent to removing the fractional part of the number, that is, taking the integer digits;
• A number is added to its own inverse value, equal to-1:

~ 3 // -4~ -3 // 2

• For an integer two consecutive binary no operations, get it itself;
• A fractional two consecutive binary no operation, can achieve the rounding effect (compared or operation, faster);
• An XOR operation can also be used to take an integer:
  12.9 ^ 0 // 12
• If you move the 0-bit to the left, it is equivalent to converting the value to a 32-bit integer, which is equivalent to rounding and valid for positive and negative numbers;
• Use the following methods to view the stored form of a negative integer inside the computer!

-1 >>> 0 // 4294967295

Binary switches

• |manufacturing masks with operations:

var mask = FLAG_A | FLAG_B | FLAG_D;// 0001 | 0010 | 1000 => 1011

• Used & to check whether the corresponding switch is turned on;

void operation

Click the link to submit the form, but do not jump to the page.

<a href=“javascript: void(document.form.submit())”>  提交</a>

Comma operator

The comma operator is used to evaluate two expressions, perform the operation before the comma, and then return the value after the comma.

var value = (console.log(‘Hi!’), true);// Hi!value // true

The function of parentheses

1. Change the priority level;
2. After the function name is placed, call this function.
   In parentheses, you can only place an expression

JavaScript Learning Experience 04