The code consists of making an array from a range of numbers and as well having a third argument in which it indicates the steps from the numbers, if it has a step of 2 well for example it goes from [1,3,5] the code works fine except when I pass step with a negative number as an argument e.g. NumberRange(10,5,-2); That's when the error appears, in the code it shows the logic I used for a negative step.

Image of the error

function NumberRange(start, end, step){
            
    var numberList = [];

    if(typeof(step) == 'undefined'){
        
        if(start < end){
            for(;start <= end; start  ){
                numberList.push(start);
            }

            console.log(numberList);
        }
        else if(start > end){
            for(;start >= end;){
                numberList.push(start);
                start -= 1;
            }
            
            console.log(numberList);
        }
    }
    else if(start > end && (Math.sign(step) == -1)){  // This is the logic I created when a negative step is given as an argument.
        for(;start >= end; start - step){
            numberList.push(start);
        }

        console.log(numberList);
    }
    else if(start < end && (Math.sign(step) == -1)){
        console.log("Negative step cant work since the value of the beginning of the list is less than the end of it")
    }
    else{
        for(;start <= end;){
            numberList.push(start);
            start  = step;
        }

        console.log(numberList);
    }

    //return numberList;
};

NumberRange(10,5,-2);

CodePudding user response：

for(;condition;) is just an ugly way of writing while(condition), don't do it.

Why it doesn't work is the for(;start >= end; start - step) part, which doesn't update start, just subtracts step from it and throws the result away. Why it wouldn't work with - is that step is negative in that branch, so it should be start = step in order to count downwards.

Generally you don't need the 4 branches, instead you could set step to /-1 if it's undefined, and if you really wanted to, you could still validate the sign of step after setting it but before using it:

function NumberRange(start, end, step) {
  if (typeof(step) == 'undefined') {
    step = Math.sign(end - start);
  }

  if (Math.sign(step) != Math.sign(end - start)) {
    console.log(`Can't count from ${start} to ${end} using ${step} as stepsize.`);
  } else {
    var numberList = [];
    if (start > end) {
      while (start > end) {
        numberList.push(start);
        start  = step;
      }
    } else {
      while (start < end) {
        numberList.push(start);
        start  = step;
      }
    }
    console.log(numberList.join());
    return numberList;
  }
}

NumberRange(10, 5, -2);
NumberRange(1, 2);
NumberRange(2, 1);
NumberRange(1, 3, 2);
NumberRange(1, 3, -2);
NumberRange(3, 1, -2);
NumberRange(3, 1, 2);

Then someone may get annoyed with having two loops with identical bodies, and after all, with a bit more complicated condition they can be collapsed into one:

function NumberRange(start, end, step) {
  if (typeof(step) == 'undefined') {
    step = Math.sign(end - start);
  }

  if (Math.sign(step) != Math.sign(end - start)) {
    console.log(`Can't count from ${start} to ${end} using ${step} as stepsize.`);
  } else {
    var numberList = [];
    while ((step > 0 && start < end) || (step < 0 && start > end)) {
      numberList.push(start);
      start  = step;
    }
    console.log(numberList.join());
    return numberList;
  }
}

NumberRange(10, 5, -2);
NumberRange(1, 2);
NumberRange(2, 1);
NumberRange(1, 3, 2);
NumberRange(1, 3, -2);
NumberRange(3, 1, -2);
NumberRange(3, 1, 2);

CodePudding user response：

You have a typo in the third for statement, the last part should be a subtraction assignment:

for(;start >= end; start  = step){
    numberList.push(start);
}

But the issue you are observing hints at an internal error in the V8 engine (a bug), probably an attempt to allocate a wrong amount of memory. I could reproduce it in Node.js and in Chrome with a simple endless loop like below.

var numberList = [];
while (true) {
    numberList.push(1);
}

On my machine, this crashes after just a few seconds, when the array contains 112813858 elements.