You should try the following:

var txt = "#div-name-1234-characteristic:561613213213";
var numb = txt.match(/\d/g);
numb = numb.join("");
console.log(numb);

The code will fail in below cases:

1. Negative numbers
2. Decimal numbers
3. Units other than px(e.g. pt, %, vw, vh, ...)

Moreover, the numbers array contains space before numbers and an empty string at the end which is not required.

I recommend to use below regex to extract numbers from strings

/[+-]?\d+(?:\.\d+)?/g

1. [+-]?: Optional + or - sign before number
2. \d+: Match one or more numbers
3. (?:\.\d+)?: Optional decimal point. ?: denotes non-capturing group.
4. g flag: To get all matches

After the numbers are extracted from string, they can be converted to Number format.

var regex = /[+-]?\d+(?:\.\d+)?/g;

var str = `padding: 0;
font-size: 16pt;
width: 50%;
height: 20vh;
margin-right: 12px;
padding-right: -12.5px;`;

var match;
while (match = regex.exec(str)) {
  console.log(match[0]);
}

Here's online demo of the regex on Regex101.

Place this string in a var, if you know every number will be seperated by a space you can easely do the following:

var string = "top 50 left 100";
    // split at the empty space
    string.split(" ");
var numbers = new Array();
// run through the array
for(var i = 0; i < string.length; i++){
    // check if the string is a number
    if(parseInt(string[i], 10)){
        // add the number to the results
        numbers.push(string[i]);
    }
}

Now you can wrap the whole bit in a function to run it at any time you want:

function extractNumbers(string){
    var temp = string.split(" ");
    var numbers = new Array();
    for(var i = 0; i < temp.length; i++){
        if(parseInt(temp[i], 10)){
            numbers.push(temp[i]);
        }
    }
    return numbers;
}

var myNumbers = extractNumbers("top 50 left 100");

Update

After reading @AmirPopovich s answer, it helped me to improve it a bit more:

if(!isNaN(Number(string[i]))){
    numbers.push(Number(string[i]));
}

This will return any type of number, not just Integers. Then you could technically extend the string prototype to extract numbers from any string:

String.prototype.extractNumbers = function(){ /*The rest of the function body here, replacing the keyword 'string' with 'this' */ };

Now you can do var result = "top 50 right 100".extractNumbers();

The solution using String.match function:

var str="(235+456+2+3-6-(2*5))"
    numbers = str.match(/\b\d+?\b/g);

console.log(numbers);  // ["235", "456", "2", "3", "6", "2", "5"]

var regex = /\d+/g;
var string = "you can enter maximum 500 choices";
var matches = string.match(regex);  // creates array from matches

document.write(matches);

References:

‌‌ ‌‌ ‌‌ ‌‌ ‌‌ ‌‌ ‌‌ ‌‌ regular-expressions.info/javascript.html (archive)

‌‌ ‌‌ ‌‌ ‌‌ ‌‌ ‌‌ ‌‌ ‌‌ developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp (archive)