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how can I remove a variable amount of characters from the end of javascript string

I've been trying to get something like this to work but it just won't:
var str = str.slice(0, -"variable");
I need to remove a variable amount of characters from the end. thanks!

Use slice:
var str = "Hello, World";
var chars = 7;
var sliced = str.slice(0, -chars);
console.log(sliced);

This -"variable" is a coercion logic, so basically you're executing something as follow: str.slice(0, NaN);
console.log(-"variable"); // js engine is trying to convert to number
Just use the variable, you don't need to wrap it with quotes like a string.
var variable = 5;
var str = "EleFromStack".slice(0, -variable);
console.log(str)

String cutting with Javascript

I have a string like "home/back/step" new string must be like "home/back".
In other words, I have to remove the last word with '/'. Initial string always has a different length, but the format is the same "word1/word2/word3/word4/word5...."

var x = "home/back/step";
var splitted = x.split("/");
splitted.pop();
var str = splitted.join("/");
console.log(str);
Take the string and split using ("/"), then remove the last element of array and re-join with ("/")

Use substr and remove everything after the last /
let str = "home/back/step";
let result = str.substr(0, str.lastIndexOf("/"));
console.log(result);

You could use arrays to remove the last word
const text = 'home/back/step';
const removeLastWord = s =>{
let a = s.split('/');
a.pop();
return a.join('/');
}
console.log(removeLastWord(text));

Seems I got a solution
var s = "your/string/fft";
var withoutLastChunk = s.slice(0, s.lastIndexOf("/"));
console.log(withoutLastChunk)

You can turn a string in javascript into an array of values using the split() function. (pass it the value you want to split on)
var inputString = 'home/back/step'
var arrayOfValues = inputString.split('/');
Once you have an array, you can remove the final value using pop()
arrayOfValues.pop()
You can convert an array back to a string with the join function (pass it the character to place in between your values)
return arrayOfValues.join('/')
The final function would look like:
function cutString(inputString) {
var arrayOfValues = inputString.split('/')
arrayOfValues.pop()
return arrayOfValues.join('/')
}
console.log(cutString('home/back/step'))

You can split the string on the '/', remove the last element with pop() and then join again the elements with '/'.
Something like:
str.split('/');
str.pop();
str.join('/');
Where str is the variable with your text.

How to convert string (number with prefix) to Double/Float in JS

How to convert a number with prefix into double/float e.g. STA01.02to 1.02?

Use regex to strip the non-numbers (excluding ".") for a more flexible solution:
parseFloat("STA01.02".replace(/[^0-9\.]+/g, ''));

// Assumed "STA0" is the fixed-length prefix, you can adjust the substring at the start you're getting rid of.
var myString = "STA01.02";
var noPrefix = myString.substring(4); // Just "1.02"
var myNumber = parseFloat(noPrefix);
console.log(myNumber); // Prints 1.02

If the prefix always the same...
var str = "STA01.02";
var number = parseFloat(str.substring(3));

split words,numbers from string and put it as 2D array in JavaScript

I have an string like'[[br,1,4,12],[f,3]]'. I want to split as strings and integers and put it into array like the string [['br',1,4,12],[f,3]].string maybe like '[]' or '[[cl,2]]',ect...but the words only,br,cl,fand i. How does get the array. Any idea for this problem?
Thanks

You can do conversion that you wanted by using RegEx :
Get your string
var str = '[[br,1,4,12],[f,3]]';
str = str.replace(/([a-zA-Z]+)/g, '"$1"');
console.log(str);
//Outputs :
[["brd",1,4,12],["f",3]] // It is still just a string
If you wanted to convert it to object, you might use this :
var str = '[[br,1,4,12],[f,3]]';
function toJSObject(str){
str = str.replace(/([a-zA-Z]+)/g, '"$1"');
return (JSON.parse(str))
}
var obj = toJSObject(str);

How to save a removed string in a new string

I have this function :
string = string.replace(/^.*?([a-zA-Z])/, '$1');
and I'd like to save both strings : the one after the expression and the one removed.
How can I do it?

<script type="text/javacript">
var str = '44234lol';
var parts = str.split(/([a-zA-Z]+)/);
alert(parts[0]);
alert(parts[1]);
</script>

This would show what was removed from the original string and what you're left with (I've altered your regex but you could use the same technique) -
var portionremoved;
var string = '1234GF'
string = string.replace(/(\d+)([A-Z]+)/,function (removed,first,second) {
portionremoved = first;
return second;
});
alert(portionremoved);
alert(string);

string1 = string.replace(/^.*?([a-zA-Z])/, '$1');
Note that string.replace returns the replaced string while string still holds the previous value.