note JavaScript Review operator

JavaScript has the following types of operators

• Assignment operators
• Comparison operators
• Arithmetic operators
• Bitwise operators
• Logical operators
• String operators
• Conditional operator
• Comma operator
• Unary operators
• Relational operator

JavaScript has binary and unary operators, and a special ternary operator (conditional operator)

Assignment Operators

An assignment operator assigns a value based on its right operand to its left operand

deconstruction

Deconstructing assignment The designing assignment syntax is a Javascript expression that can extract data from the array structure or object literal corresponding to an array or object

 var foo = ["one", "two", "three"]; //Do not use deconstruction var one   = foo[0]; var two   = foo[1]; var three = foo[2]; //Use Deconstruction var [one, two, three] = foo;

Comparison operator

A comparison operator compares its operands and returns the logical value of whether an opportunity expression is true

Operands can be numbers, strings, logic, object values

The following table describes the comparison operators in the sample code

 var var1 = 3, var2 = 4;

Arithmetic operator

Arithmetic operators use numeric values (literal quantities or variables) as operands and return a numeric value. The standard arithmetic operator is addition, subtraction, multiplication and division (+- */)

 console.log(1 / 2); /*  prints 0.5 */ console.log(1 / 2 == 1.0 / 2.0); /*  also this is true */

Bitwise Operators

Bit operators treat their operands as 32-bit binary strings (consisting of 0 and 1) rather than decimal octal or hexadecimal numbers

For example, the decimal number 9 is represented as 1001 in binary, and the bit operator performs operations on this binary representation, but the returned result is a standard JavaScript value

Bitwise logical operator

Shift Operators

The shift operator takes two operands:

• Number to be shifted
• A number that specifies how many bits to move the first number

The direction of the shift is controlled by the operator

Logical operator

Logical operators are often used between Boolean (logical) values

When all operands are boolean, the return value is also boolean

Here is && Example of the (logical AND) operator

 var a1 =  true && true;     //  t && t returns true var a2 =  true && false;    //  t && f returns false var a3 = false && true;     //  f && t returns false var a4 = false && (3 == 4); //  f && f returns false var a5 = "Cat" && "Dog";    //  t && t returns Dog var a6 = false && "Cat";    //  f && t returns false var a7 = "Cat" && false;    //  t && f returns false

Here is || Example of the (logical OR) operator

 var o1 =  true || true;     //  t || t returns true var o2 = false || true;     //  f || t returns true var o3 =  true || false;    //  t || f returns true var o4 = false || (3 == 4); //  f || f returns false var o5 = "Cat" || "Dog";    //  t || t returns Cat var o6 = false || "Cat";    //  f || t returns Cat var o7 = "Cat" || false;    //  t || f returns Cat

Here is ！ Example of the (logical NOT) operator

 var n1 = ! true;  // ! t returns false var n2 = ! false; // ! f returns true var n3 = ! "Cat"; // ! t returns false

String operator

(+) connected in series

 console.log( "my " + "string " + 2); //  "my string 2"

(+=) connected in series

 var myString = "alpha"; myString += "bet";

Conditional (ternary) operator

The conditional operator is the only operator in JavaScript that requires three operands

The result of the operation takes one of the two values according to the given conditions

 condition ?  val1 : val2

If condition is true, the result is val1; otherwise, it is val2

 var status = (age >= 18) ?  "adult" : "minor";

When age is greater than or equal to 18, the statement will "adult" Assign a value to status, otherwise it will "minor" Assign value to status

comma operator

The comma operator evaluates two operands and returns the value of the second operand

It is often used in the for loop to update multiple variables at each loop

 for (var i = 0, j = 9; i <= j; i++, j--) console.log("a[" + i + "][" + j + "]= " + a[i][j]);

 a = b = 3, c = 4; //  Returns 4 in console console.log(a); //  3 (left-most) x = (y = 5, z = 6); //  Returns 6 in console console.log(x); //  6 (right-most)

unary operator

The unary operator only corresponds to one operand

Delete operator

The delete operator deletes an object or an object's property or an element at a specified index in an array

 delete objectName; delete objectName.property; delete objectName[index]; delete property; //  legal only within a with statement

If the delete operation is successful, the attribute or element will become undefined If delete is feasible, it will return true. If it is unsuccessful, it will return false

 x = 42; var y = 43; myobj = new Number(); myobj.h = 4;    //  create property h delete x;       //  returns true (can delete if declared implicitly) delete y;       //  returns false (cannot delete if declared with var) delete Math. PI; //  returns false (cannot delete predefined properties) delete myobj.h; //  returns true (can delete user-defined properties) delete myobj;   //  returns true (can delete if declared implicitly)

also typeof 、 void

Relational Operators

In operator

If the specified property is in the specified object, true will be returned

 propNameOrNumber in objectName

Common usage of in operation

 // Arrays var trees = new Array("redwood", "bay", "cedar", "oak", "maple"); 0 in trees;        //  returns true 3 in trees;        //  returns true 6 in trees;        //  returns false "bay" in trees;    //  returns false (you must specify the index number, // not the value at that index) "length" in trees; //  returns true (length is an Array property) // Predefined objects "PI" in Math;          //  returns true var myString = new String("coral"); "length" in myString;  //  returns true // Custom objects var mycar = {make: "Honda", model: "Accord", year: 1998}; "make" in mycar;  //  returns true "model" in mycar; //  returns true

Reading materials: https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Guide

Review method: practice (write code once, run once, test once), Google where you don't understand, read and take notes

Bottom line principle: prefer rewriting once rather than copying and pasting

This review includes: operators···

Review time: it lasted for several days intermittently... I was drunk too···

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