JS code execution, will there be half of the Function A () code execution, and then to execute the Function B () code?

as mentioned, we have the following business requirements 

var x=[];

function A(){
X
}

function B(){
X
}

I"m worried now, because both function An and B are dealing with X. if there is a run-time crossover, it will cause some code logic problems.
in a database, it is generally in the form of a locked table to prevent X from being modified by both operations at the same time.
but in JS, is there any way to avoid this?
or, in other words, the way the JS code runs, this will not happen at all. It is certain that the complete code block will run before the next code block will be run.

Thank you

Javascript
Mar.10,2021

No, single thread will not appear

without the concept of and , the code will be executed, but not necessarily the result (I think that's what you're asking). For example, if there is an asynchronous method in function , it appears that An executes to a certain part of execution B and then executes A. 

var x = [];

function A() {
    setTimeout(() => {
        x[0] = 'A'
        setTimeout(() => { console.log('A', x) }, 0)
    }, 0)
}

function B() {
    setTimeout(() => {
        x[0] = 'B'
    }, 0)
}

A();
B();

the solution is the problem of asynchronous flow control. Search for a lot of it.

Previous: Use regular matching to match a string of numbers

Next: How js restricts input to enter only 4 decimal places and enter only 4 decimal places

css mysql arrays josn react html typescript webpack npm sass R objective-c .net sql-server jquery python-3.x angularjs django angular excel regex iphone ajax linux xml pandas vba spring database wordpress string wpf xcode windows bash postgresql oracle multithreading eclipse list firebase algorithm macos forms image scala visual-studio azure bootstrap spring-boot react-native python-2.7 docker performance function winforms matlab powershell apache dataframe api sqlite numpy rest shell selenium flutter dart maven loops qt swing android-studio csv express file class tensorflow sorting codeigniter perl
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b3a8eb-41264.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b3a8eb-41264.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
Need Help?