Operators of JavaScript study notes (continued)_Basic knowledge

1. Multiplicative operator

1. Multiplication: *

Some special rules for multiplication operators:

If the operands are both numerical values, they are calculated according to conventional multiplication. If the product exceeds the range of ECMAscript numerical representation, infinity or -infinity is returned
If one of the operands is NaN, the return result is NaN
If infinity is multiplied by 0, NaN
is returned. If infinity is multiplied by a non-zero number, return infinity or -infinity
Multiply infinity by infinity and return infinity
If one of the operands is not a numeric value, the background will first call number() to convert it into a numeric value, and then apply the above rules

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2. Division: /

Some special rules for division operators:

If the operands are all numerical values, they are calculated according to conventional division. If the quotient exceeds the range of ECMAscript numerical representation, infinity or -infinity is returned
If one of the operands is NaN, the return result is NaN
If infinity is divided by infinity, NaN
is returned. If 0 is divided by 0, return NaN
If a non-zero finite number is divided by 0, return infinity or -infinity
If infinity is divided by a non-zero finite number, return infinity or -infinity
If one of the operands is not a numeric value, the background will first call number() to convert it into a numeric value, and then apply the above rules

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3. Modulus (remainder): %

Some special rules for the modulo operator:

If the operands are all numeric values, follow the regular division calculation and return the remainder

If the dividend is infinite and the divisor is a finite number, the return result is NaN

If the dividend is finite and the divisor is 0, NaN
is returned If infinity is divided by infinity, NaN
is returned. If the dividend is finite and the divisor is infinite, return the dividend
If the dividend is 0, return 0
If one of the operands is not a numeric value, the background will first call number() to convert it into a numeric value, and then apply the above rules

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2. Additive operator

1. Addition operator:

If one of the operands is a string:

If both operands are strings, concatenate the second operand to the end of the first operand.
If only one operand is a string, convert the other operand into a string and then execute the above rules

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2. Subtraction operator: -

If one of the operands is a string, Boolean value, null or undefined, number() is first called in the background to convert it into a numerical value, and then subtraction is performed.

3. Relational Operators

Greater than:>

Less than:

Greater than or equal to:>=

Less than or equal to:

Special rules for relational operators:

If the operand is a string, compare the corresponding character encodings of the two strings

If one of the operands is a numerical value, convert the other operand into a numerical value first, and then compare it

When comparing any number with NaN, the result is false

4. Equality operator

1. Equality and inequality: == and! =

Both operators will convert the operands to the same type before comparison

When converting, the equality and inequality operators follow the following rules:

If one of the operands is of type Boolean, then it is first converted to a numeric type, false is converted to 0, and true is converted to 1.
If one of the operands is a string and the other is a number, the string is converted to a number for comparison.
If one of the operands is an object and the other is not, the valueof() method of the operands is called first, and then the basic type value is obtained and then compared
Special rules when comparing:

null and undefined are equal.
null and undefined are not converted to any other type
If the result of either operation is NaN, then an equality comparison returns false and an inequality comparison returns true. Note that even if both operands are NaN, the return result is still false, that is, NaN is not equal to NaN.
If both operands are objects, then the values ​​they refer to are compared, and if they refer to the same object, then return true, otherwise, return false.
2. Congruent and incongruent: == and ===

== will convert the operands into the same type for comparison;

=== will not convert types, direct comparison

For example:

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var result1 = ("55" == 55);
var result2 = ("55" === 55);
alert(result1);//true
alert(result2); //false"55" is a string, 55 is a number, the types are different

5. Conditional operators

Variable = conditional expression? True value: False value

First the conditional expression is evaluated. If the result is true, the true value is assigned to the variable. If it is false, the false value is assigned to the variable.

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6. Assignment operator

1. Simple assignment operator: =

var num1 = 10;
num=num1 10;
2. Compound assignment operators: =, -=, *=, /=, %=, >>=, >>=

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7. Comma operator

The comma operator can perform multiple operations in one statement

Purpose: 1. Declare multiple variables

var num1=1, num2=2, num3=3;

2. Assignment

var num=（0,1,2,3）//num=3

When used in assignment operations, the comma operator always returns the value of the last expression.

Practice area:

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Copy code The code is as follows:

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