I have a JS array containing numeric values:

var massiv = [
  "100", "101", "456", "1000", "321"
]

And there is a variable:

var peremennaya = "101"

Task:
if the variable matches one of the values ​​of the array, then you need to perform an action. For example:

alert = "Found 101"

The array contains only numeric values, but they are wrapped in quotes for universality, as it seems to me, i.e. so that the script does not only compare values ​​

==

but also found literal matches.

If possible, I would like to see an example with explanations of each step in the form of comments or as convenient.

Answer 1, authority 100%

Using the for

loop as an example

var massiv = [
  "100", "101", "456", "1000", "321"
]
var peremennaya = "101";
for (i = 0; i & lt; massiv.length; i ++) {
if (peremennaya == massiv [i]) {
alert ("We found" + massiv [i])
}
} 

var peremennaya = 101;
var massiv = [
  100, 101, 456, 1000, 321
];
if (massiv.indexOf (peremennaya)! = -1)
 console.log ('Array contains value' + peremennaya); 

var peremennaya = 101;
var massiv = [100, 101, 456, 1000, 321];
var itog = massiv.filter (item = & gt; {
 return item === peremennaya; // comparison logic here
});
console.log (itog); 

var testArray = [
  "100", "101", "456", "1000", "321"
]
var valueToFind = "101";
testArray.includes (valueToFind)? console.log ("find:" + valueToFind): console.log ("we didn't find anything")