how can i replace first two characters of a string in javascript? - javascript

lets suppose i have string
var string = "$-20455.00"
I am trying to swap first two characters of a string. I was thinking to split it and make an array and then replacing it, but is there any other way? Also, I am not clear how can I achieve it using arrays? if I have to use arrays.
var string = "-$20455.00"
How can I achieve this?

You can use the replace function in Javascript.
var string = "$-20455.00"
string = string.replace(/^.{2}/g, 'rr');
Here is jsfiddle: https://jsfiddle.net/aoytdh7m/33/

You dont have to use arrays. Just do this
string[1] + string[0] + string.slice(2)

You can split to an array, and then reverse the first two characters and join the pieces together again
var string = "$-20455.00";
var arr = string.split('');
var result = arr.slice(0,2).reverse().concat(arr.slice(2)).join('');
document.body.innerHTML = result;

try using the "slice" method and string concatenation:
stringpart1 = '' //fill in whatever you want to replace the first two characters of the first string with here
string2 = stringpart1 + string.slice(1)
edit: I now see what you meant by "swap". I thought you meant "swap in something else". Vlad's answer is best to just switch the first and the second character.
Note that string[0] refers to the first character in the string, and string[1] to the second character, and so on, because code starts counting at 0.

var string = "$-20455.00";
// Reverse first two characters
var reverse = string.slice(0,2).split('').reverse().join('');
// Concat again with renaming string
var result= reverse.concat(string.slice(2));
document.body.innerHTML = result;

let finalStr = string[1] + string[0] + string.slice(2); //this will give you the result

Related

Replace strings from left until the first occuring string in Javascript

I am trying to figure out how to replace example:
sw1_code1_number1_jpg --> code1_number1_jpg
hon2_noncode_number2_jpg --> noncode_number2_jpg
ccc3_etccode_number3_jpg --> etccode_number3_jpg
ddd4_varcode_number4_jpg --> varcode_number4_jpg
So the results are all string after the first _
If it doesn't find any _ then do nothing.
I know how to find and replace strings, str.replace, indexof, lastindexof but dont know how remove up to the first found occurrence.
Thank You
Use the replace method with a regular expression:
"sw1_code1_number1_jpg".replace(/^.*?_/, "");
You could split your string and get a slice
var str = 'sw1_code1_number1_jpg';
var finalStr = str.split('_').slice(1).join('_') || str;
If your original string does not contain an underscore, then it returns the original string.
UPDATE A simpler one with slice (still works with strings not containing underscores)
var str = 'sw1_code1_number1_jpg';
var finalStr = str.slice(str.indexOf('_') + 1);
This one works in all cases because when no underscore is found, -1 is returned and as we add 1 to the index we call str.slice(0) which is equal to str.
There are several approaches you can take:
var str = 'sw1_code1_number1_jpg';
var arr = str.split('_');
arr.shift();
var newSfr = arr.join('_');
Or you could use slice or replace:
var str = 'sw1_code1_number1_jpg';
var newStr = str.slice(str.indexOf('_')+1);
Or
var newStr = 'sw1_code1_number1_jpg'.replace(/^[^_]+_/,'');

How to use Javascript slice to extract first and last letter of a string?

How to use JavaScript slice to extract the first and last letter of a string?
Eg: "Hello World"
I need the result as "dH".
Following is my jsfiddle :
http://jsfiddle.net/vSAs8/
Here's the cleanest solution :
var output = input.slice(-1)+input[0];
If you want more slice, there's also
var output = input.slice(-1)+input.slice(0,1);
And here are alternate fun (and less efficient) solutions :
var output = input.replace(/^(.).*(.)$/,'$2$1');
or
var output = input.match(/^.|.$/g).reverse().join('');
Substr works as well:
alert(test.substr(-1,1) + test.substr(0,1));
a.charAt(a.length-1) + a.charAt(0)
var str = " Virat Kohali "
var get_string_label = function(str){
str = str.split(" ");
str = str.filter(res=>res.length>0);
str = str.map(function(res){
return res[0].toUpperCase();
});
str = str.join("");
return str;
};
console.log(get_string_label(str));
str.split(" "); method splits a String object into an array of strings by separating the string into substrings, where it will find space in string.
then str.filter(res=>res.length>0) will filter out string having zero length (for "virat kohali" string you will get empty sub-string)
after that using map function you can fetch your first letter

How to remove the last matched regex pattern in javascript

I have a text which goes like this...
var string = '~a=123~b=234~c=345~b=456'
I need to extract the string such that it splits into
['~a=123~b=234~c=345','']
That is, I need to split the string with /b=.*/ pattern but it should match the last found pattern. How to achieve this using RegEx?
Note: The numbers present after the equal is randomly generated.
Edit:
The above one was just an example. I did not make the question clear I guess.
Generalized String being...
<word1>=<random_alphanumeric_word>~<word2>=<random_alphanumeric_word>..~..~..<word2>=<random_alphanumeric_word>
All have random length and all wordi are alphabets, the whole string length is not fixed. the only text known would be <word2>. Hence I needed RegEx for it and pattern being /<word2>=.*/
This doesn't sound like a job for regexen considering that you want to extract a specific piece. Instead, you can just use lastIndexOf to split the string in two:
var lio = str.lastIndexOf('b=');
var arr = [];
var arr[0] = str.substr(0, lio);
var arr[1] = str.substr(lio);
http://jsfiddle.net/NJn6j/
I don't think I'd personally use a regex for this type of problem, but you can extract the last option pair with a regex like this:
var str = '~a=123~b=234~c=345~b=456';
var matches = str.match(/^(.*)~([^=]+=[^=]+)$/);
// matches[1] = "~a=123~b=234~c=345"
// matches[2] = "b=456"
Demo: http://jsfiddle.net/jfriend00/SGMRC/
Assuming the format is (~, alphanumeric name, =, and numbers) repeated arbitrary number of times. The most important assumption here is that ~ appear once for each name-value pair, and it doesn't appear in the name.
You can remove the last token by a simple replacement:
str.replace(/(.*)~.*/, '$1')
This works by using the greedy property of * to force it to match the last ~ in the input.
This can also be achieved with lastIndexOf, since you only need to know the index of the last ~:
str.substring(0, (str.lastIndexOf('~') + 1 || str.length() + 1) - 1)
(Well, I don't know if the code above is good JS or not... I would rather write in a few lines. The above is just for showing one-liner solution).
A RegExp that will give a result that you may could use is:
string.match(/[a-z]*?=(.*?((?=~)|$))/gi);
// ["a=123", "b=234", "c=345", "b=456"]
But in your case the simplest solution is to split the string before extract the content:
var results = string.split('~'); // ["", "a=123", "b=234", "c=345", "b=456"]
Now will be easy to extract the key and result to add to an object:
var myObj = {};
results.forEach(function (item) {
if(item) {
var r = item.split('=');
if (!myObj[r[0]]) {
myObj[r[0]] = [r[1]];
} else {
myObj[r[0]].push(r[1]);
}
}
});
console.log(myObj);
Object:
a: ["123"]
b: ["234", "456"]
c: ["345"]
(?=.*(~b=[^~]*))\1
will get it done in one match, but if there are duplicate entries it will go to the first. Performance also isn't great and if you string.replace it will destroy all duplicates. It would pass your example, but against '~a=123~b=234~c=345~b=234' it would go to the first 'b=234'.
.*(~b=[^~]*)
will run a lot faster, but it requires another step because the match comes out in a group:
var re = /.*(~b=[^~]*)/.exec(string);
var result = re[1]; //~b=234
var array = string.split(re[1]);
This method will also have the with exact duplicates. Another option is:
var regex = /.*(~b=[^~]*)/g;
var re = regex.exec(string);
var result = re[1];
// if you want an array from either side of the string:
var array = [string.slice(0, regex.lastIndex - re[1].length - 1), string.slice(regex.lastIndex, string.length)];
This actually finds the exact location of the last match and removes it regex.lastIndex - re[1].length - 1 is my guess for the index to remove the ellipsis from the leading side, but I didn't test it so it might be off by 1.

What is the correct pattern for splitting a string in javascript, leaving just a-z words

I have the next code that was given to me to split up a string into an array.
var chk = str.split(/[^a-z']+/i);
The problem I'm having with this solution is that if the string has a period in the end, it's being replaced with ","
For example:
If I have the next string: "hi,all-I'm-glad."
The solution above results: "hi,all,I'm,glad," (notice the "," in the end).
I need that the new string will be: "hi,all,I'm,glad"
How can I acheive it ?
Check for a . being the last character and remove it first
var str = "hi,all-I'm-glad. that you, can help,me. that-doesn't make any-sense, I know.";
if(str.charAt( str.length-1 ) == ".") {
str = str.substring(0,str.length-1);
}
var chk = str.split(/[^a-z']+/i);
console.log(chk);
var chk = str.match(/[a-z']+/gi);
console.log(chk);
You could check to see if the last element of your string array returns an empty string and remove that element
if (chk[chk.length-1] == "")
{
chk.pop();
}
var chk="to.to.".split(/[^a-z']+/i); if(chk[chk.length-1].length==0){chk.pop()}; console.log(chk);
To remove the last value of your array using pop if this one is empty.
You can utilize the pure regex power:
"hi,all-I'm-glad. that you, can help,me. that-doesn't make any-sense, I know.".replace(/[\-\.\s]/g, ',').replace(/,{2,}/g, ',').replace(/,$/,'')

Javascript split only once and ignore the rest

I am parsing some key value pairs that are separated by colons. The problem I am having is that in the value section there are colons that I want to ignore but the split function is picking them up anyway.
sample:
Name: my name
description: this string is not escaped: i hate these colons
date: a date
On the individual lines I tried this line.split(/:/, 1) but it only matched the value part of the data. Next I tried line.split(/:/, 2) but that gave me ['description', 'this string is not escaped'] and I need the whole string.
Thanks for the help!
a = line.split(/:/);
key = a.shift();
val = a.join(':');
Use the greedy operator (?) to only split the first instance.
line.split(/: (.+)?/, 2);
If you prefer an alternative to regexp consider this:
var split = line.split(':');
var key = split[0];
var val = split.slice(1).join(":");
Reference: split, slice, join.
Slightly more elegant:
a = line.match(/(.*?):(.*)/);
key = a[1];
val = a[2];
May be this approach will be the best for such purpose:
var a = line.match(/([^:\s]+)\s*:\s*(.*)/);
var key = a[1];
var val = a[2];
So, you can use tabulations in your config/data files of such structure and also not worry about spaces before or after your name-value delimiter ':'.
Or you can use primitive and fast string functions indexOf and substr to reach your goal in, I think, the fastest way (by CPU and RAM)
for ( ... line ... ) {
var delimPos = line.indexOf(':');
if (delimPos <= 0) {
continue; // Something wrong with this "line"
}
var key = line.substr(0, delimPos).trim();
var val = line.substr(delimPos + 1).trim();
// Do all you need with this key: val
}
Split string in two at first occurrence
To split a string with multiple i.e. columns : only at the first column occurrence
use Positive Lookbehind (?<=)
const a = "Description: this: is: nice";
const b = "Name: My Name";
console.log(a.split(/(?<=^[^:]*):/)); // ["Description", " this: is: nice"]
console.log(b.split(/(?<=^[^:]*):/)); // ["Name", " My Name"]
it basically consumes from Start of string ^ everything that is not a column [^:] zero or more times *. Once the positive lookbehind is done, finally matches the column :.
If you additionally want to remove one or more whitespaces following the column,
use /(?<=^[^:]*): */
Explanation on Regex101.com
function splitOnce(str, sep) {
const idx = str.indexOf(sep);
return [str.slice(0, idx), str.slice(idx+1)];
}
splitOnce("description: this string is not escaped: i hate these colons", ":")

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