use a variable in another function in javascipt

define explain outside of myFunction(), here's an example:

var explain = "yes";

myfunction() {

....

}

myfunction2() {

if ( explain == "yes") {

... } }

You have two choices: either make the variable global (or move it up to the lowest scope accessible by both functions) or pass it as an argument to the second function.

Option 1:

var explain;
function myfunction() {
    explain = "yes";
}
function myfunction2() {
    if ( explain == "yes") {
       //...
    }
}
myfunction();
myfunction2();

Option 2:

function myfunction() {
    var explain = "yes";
    myfunction2(explain);
}
function myfunction2(explain) {
    if ( explain == "yes") {
       //...
    }
}
myfunction();

You can simply make the variable in one function and call it in other function like the following:

function myfunction() {
  window.value = 'yes'; //declaring global variable by window object
}

function myfunction2() {
  console.log(window.value); //accessing global variable from other function  
  if (window.value == 'yes') {
    console.log('Run')
  }
}
myfunction();
myfunction2();

There are 2 possibilities:

1. Declare it as global.

var explain;

function myfunction() {
    explain = "yes";
}

function myfunction2() {
    if ( explain == "yes") {
         console.log('yes');
    }
}

myfunction();
myfunction2();

2. Use the variable as return and function-parameter.

function myfunction3() {
    let explain2 = "yes";
     return explain2;
}

function myfunction4(explain2) {
    if ( explain2 == "yes") {
         console.log('yes');
    }
}

let explain2 = myfunction3();
myfunction4(explain2);