JS (variable types and calculation questions in interviews)

JS (variable types and calculations)

Question 1. What types can be obtained using typeof in JS?

Question 2. When to use === When to use ==?

Question 3. What are the built-in functions in JS?

Question 4. JS variables are classified into those types according to their storage methods, and describe their characteristics?

Topic 5. How to understand JSON

1. Variable type (storage method)

1. Value type

The value type stores the value in a specific location, a stores 100, a is assigned to b, then b stores 100, changes the location of a to 200, but the location of b still stores 100.

2. Reference type

In the reference type, assign a to an object, the object exists in another place, and the memory location of a points to this place through a pointer.

In line 2, when assigning a to b, it actually defines a, and then the pointer of a points to b. After lines 1 and 2 are executed, both a and b point to the object age:20. When line 3 is executed, age The value of has become 21, and a also points to this object, so its value is also 21.

Reference types: objects, arrays, functions (features: you can add properties without restrictions. In order to let properties share memory space, the "reference" method is used)

Question 4. JS variables are classified into those types according to their storage methods, and describe their characteristics? see above

3. typeof operator