Ask user for a number, and count from that number up to 300

Question

I'm learning Javascript and created the below to take input from a user. If the number is between 150 and 300 it will print out the numbers from that number up till and including 300 in sequential order.

var num1;
conDition(); 

function conDition(){
	
	num1 = prompt("Please enter a number: "); 	

	if(num1 >= 150 && num1 <= 300){
		
    	outNum(); 

	}else if(num1 < 150){
		alert("The number is too low for this function."); 	
		num1 = 0; 
		conDition();	

	}else if(num1 > 300){
		alert("The number is too high for this function.");
		num1 = 0; 
		conDition();
		
	}else{
		alert("That is not a number!"); 
		num1 = 0;
		conDition();
	}
}

function outNum(){
	do
	{
    	document.write(num1 + "<br>");
    	num1++;
	}while (num1 <= 300);

	document.write("############################<br>");	
	return true; 
}

Can you help me make this better (more efficient)?

Answer 1

I would avoid making num1 a top level variable. Instead make it a local and pass it around. You also don't need to clear num1 every time. It will be cleared by the prompt method.

var num1 = prompt("Please enter a number: ");   
outNum(num1)
function outNum(num1) {
  ...

Instead of do..while I would recommend a for loop.

Use more meaningful variable names.

This is a minor point for a learning exercise, but if efficiency is your goal try to reduce the number of times you modify the DOM (use document.write or anything similar s it is relatively expensive.

Lastly, though it is a somewhat personal preference and there is no hard and fast rule, I dislike using recursion to solve this type of input problem.

I would write this something like:

function run() {

  while (true) { // this loop runs forever      

    var input = prompt("Please enter a number or press enter to exit: ");   
    if (!input) 
      break;        // leave the loop

    input = parseInt(input)

    if (isNaN(input)) {
        alert("That is not a number!"); 

    } else if (input < 150) {
        alert("The number is too low for this function.");  

    } else if (input > 300) {
        alert("The number is too high for this function.");

    } else {
        printNumbers(input);

    }

  }  // end of while loop

}

function printNumbers(number) {
  var output = "";

  for (; number <= 300; number++) {
    output = output + number + "<br>"
  }

  output = output + "############################<br>"; 
  document.write(output); // Just change the document once
}

run();