JavaScript Basics - Operators

JavaScript Basics - Operators (3)

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1. What is an operator

Operators, also known as operators, are symbols used to implement functions such as assignment, comparison, and arithmetic operations.

2. Expressions and return values

An expression is a combination of numbers, operators, variables, etc. that can obtain values ​​and meaningful arrangements. Generally speaking, it is a formula composed of numbers, variables, and operators. For example: 1+1=2, 100-100 = 0. From the above example, we know that the expression will have a result, which is returned to us, we call it the return value

// In the program, we often assign the return value to a variable
var sum = 12 + 34;  // Calculate the return value on the right and assign it to the variable on the left
console.log(sum); // The result is 46
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3. Overview of Arithmetic Operators

Arithmetic operators are used to perform arithmetic operations on two variables. details as follows:

  1. Addition, subtraction, multiplication, and division are similar to mathematical operations. The operator = is used to assign values ​​​​to js variables:
var x = 11; // assign 12 to the x variable
var y = 22;
var num1 = x + y; // Adds the values ​​of two variables
var num2 = x - y; // Subtract two numbers
var num3 = x * y; // multiply two numbers
var num4 = x / y; // Divide two numbers
console.log(num1); // The result is 33
console.log(num2); // -11
console.log(num3); // 242
console.log(num4); // 0.5
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Note: When calculating floating-point numbers, the output will be problematic, because the highest precision of floating-point numbers is 17 decimal places:

var num1 = 0.1;
var num2 = 0.2;
var sum = num1 + num2;
console.log(sum); // The output is 0.30000000000000004
// So two floating point numbers cannot be compared for equality
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  1. The remainder symbol is the same as the division sign in mathematics, but the two are just similar in appearance, but their functions are quite different. The remainder is to divide the two, take the remainder, and the remainder is always consistent with the sign of the dividend. The specific code is as follows:
var num1 = 15;
var num2 = 3;
var num3 = -25;
var num4 = 7;
var x = num1 % num2;
var y = num3 % num4;
console.log(x); // 0
console.log(y); // -4
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Note: If the dividend is NaN, the result is NaN.

var result = NaN % 2;
console.log(result); // The result is NaN
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4. Assignment operator

Assignment operators are used to assign values ​​to JavaScript variables, as follows: 

// = is direct assignment
var num = 15;
// +=, -=, *=, /=, %= is the first operation and then assignment
num += 1; // Equivalent to num = num + 1
num -= 1; // Equivalent to num = num - 1
num *= 10; // Equivalent to num = num * 10
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5. Increment and Decrement Operators

5.1 Overview of increment and decrement operators

To repeatedly add or subtract one to a numeric variable, you can use the increment operator ( ++ ) and the decrement operator ( – ). In js, the increment and decrement operators can be placed in front of the variable or in the After the variable, note that it must be used in conjunction with the variable:

  • When placed in front of a variable, we call it a pre-increment (decrement) operator
  • After the variable is what we call the post-increment (decrement) operator

5.2 Increment operator

5.2.1 Pre-increment operator

The pre-increment operator is written in front of the variable, such as: ++num, which means self-increment, which is equivalent to num = num + 1, but ++num is simpler.

var age = 18;
++age; // Equivalent to age = age + 1
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5.2.2 Post-increment operator

The post-increment operator is written after the variable, which also means self-increment, and the writing method is simpler. It returns the original value first and then self-increment.

var age = 20;
age++; // Equivalent to age = age + 1
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5.2.3 Difference between Postfix and Prefix Operators

If the two are used alone, the effect is the same, but there is a little difference in the calculation process. When used with other codes, the execution results will be different. The preposition is to return the value after the self-increment, and the postposition is to return the value first, and then Add from:

// pre-increment operator
var num = 10;
console.log(++num + 1); // The result is 12, because num first increases from 1 to 11, returns, and adds 1
// post-increment operator
var age = 15;
console.log(age++ + 5); // The result is 20, because the postfix returns the original value first, and then adds 1
console.log(age); // The result is 16, which is the result of self-addition
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Note: Post-increment (decrement) operators are generally used in development.

6. Comparison Operators

Comparison operators are used for comparison between two data, and the operation result is a Boolean value 

console.log(2 == 4); // false
console.log(54 <= 134); // true
console.log(19 === '19'); // false, the congruent symbol requires that the values ​​and data types on both sides are exactly the same to be true (true)
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7. Logical operators

7.1 Overview of Logical Operators

Logical operators are mainly used to perform Boolean operations, and their return values ​​are Boolean values, which are mainly used for conditional judgment:

7.2 Logical AND

&& (logical AND) returns true only if the values ​​on both sides are true, otherwise returns false

var result = 2 > 1 && 5 > 3; // true
var outcome = 10 > 100 && 4 > 1; // false
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7.3 Logical OR

|| (logical OR) returns true as long as one of them is true, and returns false if both sides are false

var result = 34 > 12 || 12 > 34; // true
var outcome = 23 < 12 || 56 < 45; // false
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7.4 Logical NOT

Logical not (!) is also called negation, which is used to take the opposite value of a Boolean value, such as the opposite value of true is false

var sayOk = !true;
console.log(sayOk); // false
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7.5 Logic and short-circuit operation (logic interrupt)

Short-circuit operation: When there are multiple expressions (values), the value of the expression on the left can be determined, and the expression on the right will not be evaluated.

Logical and short-circuit operations:

  • Syntax: expression1 && expression2
  • If expression 1 is true, return expression 2 (true return other)
  • If expression1 is false, return expression1 (return from false from)
console.log(0 && 23); // The result is 0, since 0 is false, return 0 itself
console.log(123 && 356); // The result is 356, since 123 is true, returns 356
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7.6 Logical or short-circuit operation

  • Syntax: expression1 || expression2
  • If expression1 is true, return expression1 (return true from)
  • If expression 1 is false, return expression 2 (return other from false)
console.log(123 && 345); // The result is 123
console.log(0 && 467); // 467
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7.7 Application of short-circuit calculation

Logical interruption is very important, it will directly affect the running results of the program:

var age = 18;
console.log(345 || age++); // 345 is true, return, do not execute age++
console.log(age); // The value is still 18, because age++ is not executed
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8. Operator precedence

  • Logical AND has a higher priority than logical OR
  • Logical non-precedence in unary operators is high
  • Higher priority first, then lower priority
  • Equal priority is counted from left to right

Tags: Javascript

Posted by Zanus on Sat, 31 Dec 2022 19:41:29 +1030

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