How to quickly get started with VUE3.0: Enter learning
1.
Thinking about the scope of variables: After declaring a variable, can it be used anywhere?
Answer: No.
Example: Variables declared with the var keyword within a function cannot be accessed outside the function.
Summary : The use of variables has a scope.
Scope division: global scope, function scope and block-level scope (provided by ES6).
Variables corresponding to different scopes: global variables, local variables, block-level variables (provided by ES6).
Global variables : Variables that are not declared within any function (explicit definition) or variables declared within a function by omitting var (implicit definition) are called global variables.
Scope: It can be used in all scripts in the same page file.
Local variables : Variables defined using the var keyword in a function body are called local variables, which are only valid within the function body.
Block-level variables : Variables declared by the let keyword provided by ES6 are called block-level variables, which are only valid between "{}", such as if, for, or while statements, etc.
Garbage collection mechanism
In JavaScript, local variables only exist during the execution of a function. During this process, local variables will be allocated corresponding space on the (stack or heap) memory to store their values, and then in the function These variables are used until the end of the function. Once the function execution ends, there is no need for local variables to exist. At this time, JavaScript will automatically release the memory space they occupy through the garbage collection mechanism.
If you want to retain the value of local variables during development, you can achieve this in the following two ways:
2.
The concept of anonymous function: The so-called function expression refers to assigning the declared function to a variable, and completing the function call and parameter transfer through the variable. It is also another way to implement custom functions in JavaScript.
concept: Anonymous function refers to a function without a function name.
Function: It can effectively avoid the pollution of global variables and the conflict of function names.
Note: It is not only another representation of function expression, but also can be called through function declaration.
concept: ES6 introduces a new syntax for writing anonymous functions, which we call arrow functions.
Features: The syntax of an arrow function expression is shorter than that of a function expression.
3. Nested and recursive
What is a nested function: It is a declaration that another function exists inside a function.
Features: The inner function can only be executed within the scope of the outer function. During the execution of the inner function, if a variable needs to be introduced, it will first be searched in the current scope. If not found, it will continue to the next higher level. Searching in the scope until the global scope, we call this chain query relationship a scope chain.
concept: Recursive call is a special kind of call in nested function calls. It refers to the process of a function calling itself within its function body. This type of function is called a recursive function.
The following is an example of calculating factorial.
Note
that although recursive calling is very suitable when traversing multi-dimensional arrays with variable dimensions, it takes up a lot of memory and resources and is difficult to implement and maintain. Therefore, recursive calling of functions should be used with caution in development.
Study Find the value of the Nth term of the Fibonacci sequence.
Understand what the Fibonacci sequence
is
. The Fibonacci sequence is also called the golden section sequence, such as “1, 1, 2, 3, 5, 8, 13, 21…".
Find the pattern: This sequence starts with the 3rd item, and each item is equal to the sum of the previous two items.
Ifthe code implementation idea