Arithmetic operation

1. Add +

A, spell list

Concept: Manipulating different types of data and strings concatenates strings.

1, if the character is added, will “string”

result = "123" + "456";
console.log("result=" + result); // result=123456
console.log("Result type :" + typeof(result)); // Result type :string
Copy the code

2. Any type and character added will be converted to a string and then assembled

var result = "Hello" + 123; Result = "Hello" +"123"; // result = "Hello" +"123";
console.log("result=" + result); // result=Hello123
console.log("Result type :" + typeof(result)); // Result type :string
Copy the code

⚠️ Note: the result of the concatenation has nothing to do with the expression of the concatenation of the two types but rather with the expression of the string itself

🚀T- Tests whether the influence factor of the concatenation string result is related to the string form or concatenation form.

1) Change the stitching form

// There is no obvious space
result = "Hello" + 123;
// Clear space
result = "Hello"     +      123;
/ / no Spaces
result = "Hello"+123;
Copy the code

The result is always result=Hello123

2) Change the string itself

result = "Hello " + 123;
Copy the code

Results the result = Hello 123

Based on this feature

So you can use this method to convert other data types to strings

result =  "Hello"  + "";
Copy the code

⚠️ Note: Order of addition operations, from left to right

2. The subtraction –

Except for the string in addition, all operations convert other data types to the Number data type

3. * multiplication

1. Ground rules

1, undefined to number equals NaN

var result = 2*undefined;
console.log("result=" + result); // result=NaN
console.log("Result type =" + typeof(result)); // Result type ==number
Copy the code

2. Null converts number to 0

result = 2 * null ;
console.log("result=" + result); // result=0
console.log("Result type =" + typeof(result)); // Result type =number
Copy the code

Any value that does the – * / operation becomes the number data type. You can use this feature to convert other data types to the number data type.

4. The division /

. slightly

(after)

The operator

1. Unary operators

– sign For non-number values, the addition of a – sign becomes a number value

If a =true ;
         a  = -a ;
console.log(typeof  a);  / / output number
consle.log(  a );   / / output 1
Copy the code

You can use + on any other data type, where + is the unary operator, to turn it into the number data type, just like the number () function

2. Logical operators

1,! non

Concept: take the negative of a non-Boolean value, first change the non-Boolean value to a Boolean value type and then take the negative. You can convert any data type to a Boolean type, just as the Boolean () function does, but implicitly

2, && and

Concept: Return false whenever there is a false (both 1 and 0 are 1 and 0 are 0).

Understanding: As with love, as long as one person is not true, it is not true love, both are true love.

3, | | or

Concept: Return true as long as one of them is true(both 0 and 1 are 0)

Understanding: as affection, as long as there is a person to love you, all for affection

(after)

3. The non-Boolean or and operator

Method: convert to Boolean and then evaluate, and return the original value.

Two cases

1. && operation

If the first value is true, the following values are returned:

If the first value of 2&&3 is 2, it is true. According to the principle, if 1 is 1 and 0 is 0, the result can be judged only by looking at the last number in both cases.

a = 2&&3 / / 3
Copy the code

If the first is false, the first value is returned directly:

If the first value of 0&&3 is 0, it is false. According to the principle, if 1 is 1, any 0 is 0, regardless of whether the following value is true or false, the result is false, so you can judge the result by looking at the first value. This phenomenon is also known as “short-circuiting”.

a =   0&&2; / / 0
Copy the code

2. | | operation

If the first value is true, return the first value [short circuit]

If the first value is false, the second value is returned

Summary:

  • Am& : the short-circuit value is false, so return the first value if the first value is false.
  • | | operation: the value of the short-circuit is true, so the first value is true, it returns the first value

(after)

4. The assignment operator

Copy operations: + =, -=, *= /, / =, % =

5. Relational operators

Temporary slightly…