JavaScript study notes operators_basic knowledge

1. Unary operators

1. Auto-increment and decrement operators: divided into pre-positioned and post-positioned types;

Front type: a;--a;

Post type: a ;a--;

Example:

Copy code The code is as follows:

where a=i, equivalent to a=i;i=i 1;
And b= j, which is equivalent to j=j 1;b=j;

2. Unary addition and subtraction operators: a= i;a=-i;

Copy code The code is as follows:

For integers, subtracting one dollar is equivalent to taking a negative number.

2. Bit operators

1. Bitwise NOT~ (NOT)

No, that is, invert all numbers in binary form.

Common usage: Bitwise operation NOT is essentially to negate a number and then subtract 1

2. Bitwise OR | (OR)

Or, that is, perform a bitwise OR operation on all numbers and the target number in binary form.

Common usage: Usually used for unconditional assignment of binary numbers. For example: a number |1 is equivalent to getting the odd number closest to the current number.

3. Bitwise AND (AND)

And, that is, perform a bitwise AND operation on all numbers and the target number in binary form.

Common usage: Usually used for binary bit-taking operations, for example: a number &1, if the result is 0, it is an even number, if it is 1, it is an odd number.

4. Bitwise XOR^ (XOR)

XOR, that is, compare all numbers with the target number in binary form. If only two numbers are different, that is, only one digit stores a 1, 1 will be returned. If the two numbers are the same, 0 will be returned.

Common usage: The inverse operation of xor operation is itself, that is to say, the final result of XORing the same number twice remains unchanged. Can be used for simple encryption, or interactive numerical operations.

5. Move left<<

Shift left, that is, move all numbers to the left by the corresponding number of digits in binary form, shift out (discard) the high bits, and fill in the empty bits of the low bits with zeros. Left shifting does not affect the sign bit.

Mathematical meaning: As long as the number does not overflow, for positive and negative numbers, shifting one position to the left is equivalent to multiplying by 2 raised to the power of 1, and shifting n bits to the left is equivalent to multiplying by 2 raised to the nth power.

6. Move right

6.1 Signed right shift>>: Shift all values ​​to the right in binary form but retain the sign bit.

Mathematical meaning: As long as the number does not overflow, for positive and negative numbers, shifting one position to the right is equivalent to dividing by 2 to the power of 1, and shifting to the right by n bits is equivalent to dividing by 2 to the nth power.

6.2 Unsigned right shift>>>: That is, moving all values, including the sign bit, to the right in binary form.

For positive numbers, the results of >> and >>> are the same;

For negative numbers, since negative numbers are represented in the complement form of their absolute value, the unsigned right shift result will be very large.

3. Boolean operators

1. Logical negation!
Logic is useless! Indicates that it can be applied to any type of value in ECMAScript. The logical NOT operation returns a Boolean value (true/false). This operator first converts its operand to a Boolean value and then negates it.

! ! Equivalent to the Boolean() function.

A set of rules for the Boolean() transformation function.

Data type Convert to true value Convert to false value
Boolean true false
String Any non-empty string ""(empty string)
Number Any non-zero numeric value (including infinity) 0 and NaN
Object any object null
Undefined None undefined

2. Logical AND&&

Logical AND has two operands.

Logical AND operations can be applied to any type of operand, not just Boolean values. In the case where one of the operands is not a Boolean value, the logical AND operation does not necessarily return a Boolean value; in this case, it follows the following rules:
1. If the first operand is an object, return the second operand;
2. If the second operand is an object, the object will be returned only if the evaluation result of the first operand is true;
3. If both operators are objects, return the second operand; follow the first rule.
4. If one of the operands is null, return null;
5. If one of the operands is NaN, return NaN;
6. If one of the operands is undefined, return undefined.

The logical AND operation is a short-circuit operation, that is, if the first operand can determine the result, then the second operand will not be evaluated. (Can be understood as two internal return operations). Therefore, when rules 4, 5, and 6 conflict, the short-circuit operation principle shall be followed.

Copy code The code is as follows:

var nul = null;
var na = NaN;
var test;
test = na&&nul;
document.write(test); //NaN

Copy code The code is as follows:

var nul = null;
var na = NaN;
var test;
test = nul&&na;
document.write(test); //null

3. Logical OR||

Logical OR has two operands.

Logical OR is similar to logical AND in that the operation can be applied to any type of operand, not just Boolean values. In the case where one of the operands is not a Boolean value, the logical OR operation does not necessarily return a Boolean value; in this case, it follows the following rules:
1. If the first operand is an object, return the first operand;
2. If the result of the first operand is false, return the second operand;
3. If both operators are objects, the first operand is returned, following the first rule.
4. If both operands are null, return null;
5. If both operands are NaN, return NaN;
6. If both operands are undefined, return undefined.

The logical OR operation is a short-circuit operation, that is, if the result of the first operand is true, then the second operand will not be evaluated again.

We can use this feature of logical OR to avoid assigning null or undefined values ​​to variables

For example: var myObject=firstObject||secondObject

If firstObject is not null, firstObject is assigned to myObject, otherwise the value of secondObject is assigned to myObject.

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