JavaScript closure inside loops – simple practical example

var funcs = [];
// let's create 3 functions
for (var i = 0; i < 3; i++) {
// and store them in funcs
funcs[i] = function() {
// each should log its value.
console.log("My value:", i);
};
}
for (var j = 0; j < 3; j++) {
// and now let's run each one to see
funcs[j]();
}

My value: 3
My value: 3
My value: 3

My value: 0
My value: 1
My value: 2

var buttons = document.getElementsByTagName("button");
// let's create 3 functions
for (var i = 0; i < buttons.length; i++) {
// as event listeners
buttons[i].addEventListener("click", function() {
// each should log its value.
console.log("My value:", i);
});
}
<button>0</button>
<br />
<button>1</button>
<br />
<button>2</button>

// Some async wait function
const wait = (ms) => new Promise((resolve, reject) => setTimeout(resolve, ms));

for (var i = 0; i < 3; i++) {
// Log `i` as soon as each promise resolves.
wait(i * 100).then(() => console.log(i));
}

const arr = [1,2,3];
const fns = [];

for (var i in arr){
fns.push(() => console.log("index:", i));
}

for (var v of arr){
fns.push(() => console.log("value:", v));
}

for (const n of arr) {
var obj = { number: n }; // or new MyLibObject({ ... })
fns.push(() => console.log("n:", n, "|", "obj:", JSON.stringify(obj)));
}

for(var f of fns){
f();
}