You can use the substring function:

let str = "12345.00";
str = str.substring(0, str.length - 1);
console.log(str);

This is the accepted answer, but as per the conversations below, the slice syntax is much clearer:

let str = "12345.00";
str = str.slice(0, -1); 
console.log(str);

You can use slice! You just have to make sure you know how to use it. Positive #s are relative to the beginning, negative numbers are relative to the end.

js>"12345.00".slice(0,-1)
12345.0

You can use the substring method of JavaScript string objects:

s = s.substring(0, s.length - 4)

It unconditionally removes the last four characters from string s.

However, if you want to conditionally remove the last four characters, only if they are exactly _bar:

var re = /_bar$/;
s.replace(re, "");

The easiest method is to use the slice method of the string, which allows negative positions (corresponding to offsets from the end of the string):

const s = "your string";
const withoutLastFourChars = s.slice(0, -4);

If you needed something more general to remove everything after (and including) the last underscore, you could do the following (so long as s is guaranteed to contain at least one underscore):

const s = "your_string";
const withoutLastChunk = s.slice(0, s.lastIndexOf("_"));
console.log(withoutLastChunk);

For a number like your example, I would recommend doing this over substring:

console.log(parseFloat('12345.00').toFixed(1));

Do note that this will actually round the number, though, which I would imagine is desired but maybe not:

console.log(parseFloat('12345.46').toFixed(1));

Be aware that String.prototype.{ split, slice, substr, substring } operate on UTF-16 encoded strings

None of the previous answers are Unicode-aware. Strings are encoded as UTF-16 in most modern JavaScript engines, but higher Unicode code points require surrogate pairs, so older, pre-existing string methods operate on UTF-16 code units, not Unicode code points. See: Do NOT use .split('').

const string = "ẞ🦊";

console.log(string.slice(0, -1)); // "ẞ\ud83e"
console.log(string.substr(0, string.length - 1)); // "ẞ\ud83e"
console.log(string.substring(0, string.length - 1)); // "ẞ\ud83e"
console.log(string.replace(/.$/, "")); // "ẞ\ud83e"
console.log(string.match(/(.*).$/)[1]); // "ẞ\ud83e"

const utf16Chars = string.split("");

utf16Chars.pop();
console.log(utf16Chars.join("")); // "ẞ\ud83e"

In addition, RegExp methods, as suggested in older answers, don’t match line breaks at the end:

const string = "Hello, world!\n";

console.log(string.replace(/.$/, "").endsWith("\n")); // true
console.log(string.match(/(.*).$/) === null); // true

Use the string iterator to iterate characters

Unicode-aware code utilizes the string’s iterator; see Array.from and ... spread. string[Symbol.iterator] can be used (e.g. instead of string) as well.

Also see How to split Unicode string to characters in JavaScript.

Examples:

const string = "ẞ🦊";

console.log(Array.from(string).slice(0, -1).join("")); // "ẞ"
console.log([
  ...string
].slice(0, -1).join("")); // "ẞ"

Use the s and u flags on a RegExp

The dotAll or s flag makes . match line break characters, the unicode or u flag enables certain Unicode-related features. Note that, when using the u flag, you eliminate unnecessary identity escapes, as these are invalid in a u regex, e.g. \[ is fine, as it would start a character class without the backslash, but \: isn’t, as it’s a : with or without the backslash, so you need to remove the backslash.

Examples:

const unicodeString = "ẞ🦊",
  lineBreakString = "Hello, world!\n";

console.log(lineBreakString.replace(/.$/s, "").endsWith("\n")); // false
console.log(lineBreakString.match(/(.*).$/s) === null); // false
console.log(unicodeString.replace(/.$/su, "")); // ẞ
console.log(unicodeString.match(/(.*).$/su)[1]); // ẞ

// Now `split` can be made Unicode-aware:

const unicodeCharacterArray = unicodeString.split(/(?:)/su),
  lineBreakCharacterArray = lineBreakString.split(/(?:)/su);

unicodeCharacterArray.pop();
lineBreakCharacterArray.pop();
console.log(unicodeCharacterArray.join("")); // "ẞ"
console.log(lineBreakCharacterArray.join("").endsWith("\n")); // false

Note that some graphemes consist of more than one code point, e.g. 🏳️‍🌈 which consists of the sequence 🏳 (U+1F3F3), VS16 (U+FE0F), ZWJ (U+200D), 🌈 (U+1F308). Here, even Array.from will split this into four “characters”. Matching those is made easier with the RegExp set notation and properties of strings proposal.

Using JavaScript's slice function:

let string = 'foo_bar';
string = string.slice(0, -4); // Slice off last four characters here
console.log(string);

This could be used to remove '_bar' at end of a string, of any length.

A regular expression is what you are looking for:

let str = "foo_bar";
console.log(str.replace(/_bar$/, ""));

Try this:

const myString = "Hello World!";
console.log(myString.slice(0, -1));

Performance

Today 2020.05.13 I perform tests of chosen solutions on Chrome v81.0, Safari v13.1 and Firefox v76.0 on MacOs High Sierra v10.13.6.

Conclusions

• the slice(0,-1)(D) is fast or fastest solution for short and long strings and it is recommended as fast cross-browser solution
• solutions based on substring (C) and substr(E) are fast
• solutions based on regular expressions (A,B) are slow/medium fast
• solutions B, F and G are slow for long strings
• solution F is slowest for short strings, G is slowest for long strings

Details

I perform two tests for solutions A, B, C, D, E(ext), F, G(my)

• for 8-char short string (from OP question) - you can run it HERE
• for 1M long string - you can run it HERE

Solutions are presented in below snippet

function A(str) {
  return str.replace(/.$/, '');
}

function B(str) {
  return str.match(/(.*).$/)[1];
}

function C(str) {
  return str.substring(0, str.length - 1);
}

function D(str) {
  return str.slice(0, -1); 
}

function E(str) {
  return str.substr(0, str.length - 1);
}

function F(str) {
  let s= str.split("");
  s.pop();
  return s.join("");
}

function G(str) {
  let s='';
  for(let i=0; i<str.length-1; i++) s+=str[i];
  return s;
 }



// ---------
// TEST
// ---------

let log = (f)=>console.log(`${f.name}: ${f("12345.00")}`);

[A,B,C,D,E,F,G].map(f=>log(f));

This snippet only presents soutions

Here are example results for Chrome for short string

https://stackoverflow.com/questions/34817546/javascript-how-to-delete-last-two-characters-in-a-string

Just use trim if you don't want spaces

"11.01 °C".slice(0,-2).trim()

Use regex:

let aStr = "12345.00";
aStr = aStr.replace(/.$/, '');
console.log(aStr);

How about:

let myString = "12345.00";
console.log(myString.substring(0, myString.length - 1));

1. (.*), captures any character multiple times:

console.log("a string".match(/(.*).$/)[1]);

2. ., matches last character, in this case:

console.log("a string".match(/(.*).$/));

3. $, matches the end of the string:

console.log("a string".match(/(.*).{2}$/)[1]);

Here is an alternative that i don't think i've seen in the other answers, just for fun.

var strArr = "hello i'm a string".split("");
strArr.pop();
document.write(strArr.join(""));

Not as legible or simple as slice or substring but does allow you to play with the string using some nice array methods, so worth knowing.

debris = string.split("_") //explode string into array of strings indexed by "_"

debris.pop(); //pop last element off the array (which you didn't want)

result = debris.join("_"); //fuse the remainng items together like the sun

If you want to do generic rounding of floats, instead of just trimming the last character:

var float1 = 12345.00,
    float2 = 12345.4567,
    float3 = 12345.982;

var MoreMath = {
    /**
     * Rounds a value to the specified number of decimals
     * @param float value The value to be rounded
     * @param int nrDecimals The number of decimals to round value to
     * @return float value rounded to nrDecimals decimals
     */
    round: function (value, nrDecimals) {
        var x = nrDecimals > 0 ? 10 * parseInt(nrDecimals, 10) : 1;
        return Math.round(value * x) / x;
    }
}

MoreMath.round(float1, 1) => 12345.0
MoreMath.round(float2, 1) => 12345.5
MoreMath.round(float3, 1) => 12346.0

EDIT: Seems like there exists a built in function for this, as Paolo points out. That solution is obviously much cleaner than mine. Use parseFloat followed by toFixed

if(str.substring(str.length - 4) == "_bar")
{
    str = str.substring(0, str.length - 4);
}

Via slice(indexStart, indexEnd) method - note, this does NOT CHANGE the existing string, it creates a copy and changes the copy.

console.clear();
let str = "12345.00";
let a = str.slice(0, str.length -1)
console.log(a, "<= a");
console.log(str, "<= str is NOT changed");

Via Regular Expression method - note, this does NOT CHANGE the existing string, it creates a copy and changes the copy.

console.clear();
let regExp = /.$/g
let b = str.replace(regExp,"")
console.log(b, "<= b");
console.log(str, "<= str is NOT changed");

Via array.splice() method -> this only works on arrays, and it CHANGES, the existing array (so careful with this one), you'll need to convert a string to an array first, then back.

console.clear();
let str = "12345.00";
let strToArray = str.split("")
console.log(strToArray, "<= strToArray");
let spliceMethod = strToArray.splice(str.length-1, 1)
str = strToArray.join("")
console.log(str, "<= str is changed now");

In cases where you want to remove something that is close to the end of a string (in case of variable sized strings) you can combine slice() and substr().

I had a string with markup, dynamically built, with a list of anchor tags separated by comma. The string was something like:

var str = "<a>text 1,</a><a>text 2,</a><a>text 2.3,</a><a>text abc,</a>";

To remove the last comma I did the following:

str = str.slice(0, -5) + str.substr(-4);

You can, in fact, remove the last arr.length - 2 items of an array using arr.length = 2, which if the array length was 5, would remove the last 3 items.

Sadly, this does not work for strings, but we can use split() to split the string, and then join() to join the string after we've made any modifications.

var str = 'string'

String.prototype.removeLast = function(n) {
  var string = this.split('')
  string.length = string.length - n

  return string.join('')
}

console.log(str.removeLast(3))

Try to use toFixed

const str = "12345.00";
return (+str).toFixed(1);

Try this:

<script>
    var x="foo_foo_foo_bar";
    for (var i=0; i<=x.length; i++) {
        if (x[i]=="_" && x[i+1]=="b") {
            break;
        }
        else {
            document.write(x[i]);
        }
    }
</script>

You can also try the live working example on http://jsfiddle.net/informativejavascript/F7WTn/87/.

@Jason S:

You can use slice! You just have to make sure you know how to use it. Positive #s are relative to the beginning, negative numbers are relative to the end.

js>"12345.00".slice(0,-1) 12345.0

Sorry for my graphomany but post was tagged 'jquery' earlier. So, you can't use slice() inside jQuery because slice() is jQuery method for operations with DOM elements, not substrings ... In other words answer @Jon Erickson suggest really perfect solution.

However, your method will works out of jQuery function, inside simple Javascript. Need to say due to last discussion in comments, that jQuery is very much more often renewable extension of JS than his own parent most known ECMAScript.

Here also exist two methods:

as our:

string.substring(from,to) as plus if 'to' index nulled returns the rest of string. so: string.substring(from) positive or negative ...

and some other - substr() - which provide range of substring and 'length' can be positive only: string.substr(start,length)

Also some maintainers suggest that last method string.substr(start,length) do not works or work with error for MSIE.

Use substring to get everything to the left of _bar. But first you have to get the instr of _bar in the string:

str.substring(3, 7);

3 is that start and 7 is the length.