Javascript Form validation | set a specific input format -

i'm working on project has input field requiring user enter of following 3 options:

1. number 150
2. number starting 1 letter (which must n, not case sensitive) n150
3. number ending 1 letter (which must n, not case sensitive) 150n

any other value like:

• 150x return error message wrong input
• x150 return wrong input
• 1n50 return wrong position

the correct way make array of valid numbers , check if given text exists on array.
for example:

var validnumbers = [ 150, n150, 150n ];  if (validnumbers.indexof(parseint(num, 10)) >=0 ) {     //match } 

you'll need indexof function ie:

if (!array.prototype.indexof) { array.prototype.indexof = function(needle) {     for(var = 0; < this.length; i++) {         if(this[i] === needle) {             return i;         }     }     return -1; }; }