问题
Does anyone know of a Javascript library (e.g. underscore, jQuery, MooTools, etc.) that offers a method of incrementing a letter?
I would like to be able to do something like:
\"a\"++; // would return \"b\"
回答1:
Simple, direct solution
function nextChar(c) {
return String.fromCharCode(c.charCodeAt(0) + 1);
}
nextChar('a');
As others have noted, the drawback is it may not handle cases like the letter 'z' as expected. But it depends on what you want out of it. The solution above will return '{' for the character after 'z', and this is the character after 'z' in ASCII, so it could be the result you're looking for depending on what your use case is.
Unique string generator
(Updated 2019/05/09)
Since this answer has received so much visibility I've decided to expand it a bit beyond the scope of the original question to potentially help people who are stumbling on this from Google.
I find that what I often want is something that will generate sequential, unique strings in a certain character set (such as only using letters), so I've updated this answer to include a class that will do that here:
class StringIdGenerator {
constructor(chars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ') {
this._chars = chars;
this._nextId = [0];
}
next() {
const r = [];
for (const char of this._nextId) {
r.unshift(this._chars[char]);
}
this._increment();
return r.join('');
}
_increment() {
for (let i = 0; i < this._nextId.length; i++) {
const val = ++this._nextId[i];
if (val >= this._chars.length) {
this._nextId[i] = 0;
} else {
return;
}
}
this._nextId.push(0);
}
*[Symbol.iterator]() {
while (true) {
yield this.next();
}
}
}
Usage:
const ids = new StringIdGenerator();
ids.next(); // 'a'
ids.next(); // 'b'
ids.next(); // 'c'
// ...
ids.next(); // 'z'
ids.next(); // 'A'
ids.next(); // 'B'
// ...
ids.next(); // 'Z'
ids.next(); // 'aa'
ids.next(); // 'ab'
ids.next(); // 'ac'
回答2:
Plain javascript should do the trick:
String.fromCharCode('A'.charCodeAt() + 1) // Returns B
回答3:
What if the given letter is z? Here is a better solution. It goes A,B,C... X,Y,Z,AA,AB,... etc. Basically it increments letters like the column ID's of an Excel spreadsheet.
nextChar('yz'); // returns "ZA"
function nextChar(c) {
var u = c.toUpperCase();
if (same(u,'Z')){
var txt = '';
var i = u.length;
while (i--) {
txt += 'A';
}
return (txt+'A');
} else {
var p = "";
var q = "";
if(u.length > 1){
p = u.substring(0, u.length - 1);
q = String.fromCharCode(p.slice(-1).charCodeAt(0));
}
var l = u.slice(-1).charCodeAt(0);
var z = nextLetter(l);
if(z==='A'){
return p.slice(0,-1) + nextLetter(q.slice(-1).charCodeAt(0)) + z;
} else {
return p + z;
}
}
}
function nextLetter(l){
if(l<90){
return String.fromCharCode(l + 1);
}
else{
return 'A';
}
}
function same(str,char){
var i = str.length;
while (i--) {
if (str[i]!==char){
return false;
}
}
return true;
}
// below is simply for the html sample interface and is unrelated to the javascript solution
var btn = document.getElementById('btn');
var entry = document.getElementById('entry');
var node = document.createElement("div");
node.id = "node";
btn.addEventListener("click", function(){
node.innerHTML = '';
var textnode = document.createTextNode(nextChar(entry.value));
node.appendChild(textnode);
document.body.appendChild(node);
});<input id="entry" type="text"></input>
<button id="btn">enter</button>回答4:
You can try this
console.log( 'a'.charCodeAt(0))
First convert it to Ascii number .. Increment it .. then convert from Ascii to char..
var nex = 'a'.charCodeAt(0);
console.log(nex)
$('#btn1').on('click', function() {
var curr = String.fromCharCode(nex++)
console.log(curr)
});
Check FIDDLE
回答5:
I needed to use sequences of letters multiple times and so I made this function based on this SO question. I hope this can help others.
function charLoop(from, to, callback)
{
var i = from.charCodeAt(0);
var to = to.charCodeAt(0);
for(;i<=to;i++) callback(String.fromCharCode(i));
}
- from - start letter
- to - last letter
- callback(letter) - function to execute for each letter in the sequence
How to use it:
charLoop("A", "K", function(char) {
//char is one letter of the sequence
});
See this working demo
回答6:
Adding upon all these answers:
// first code on page
String.prototype.nextChar = function(i) {
var n = i | 1;
return String.fromCharCode(this.charCodeAt(0) + n);
}
String.prototype.prevChar = function(i) {
var n = i | 1;
return String.fromCharCode(this.charCodeAt(0) - n);
}
Example: http://jsfiddle.net/pitaj/3F5Qt/
回答7:
One possible way could be as defined below
function incrementString(value) {
let carry = 1;
let res = '';
for (let i = value.length - 1; i >= 0; i--) {
let char = value.toUpperCase().charCodeAt(i);
char += carry;
if (char > 90) {
char = 65;
carry = 1;
} else {
carry = 0;
}
res = String.fromCharCode(char) + res;
if (!carry) {
res = value.substring(0, i) + res;
break;
}
}
if (carry) {
res = 'A' + res;
}
return res;
}
console.info(incrementString('AAA')); // will print AAB
console.info(incrementString('AZA')); // will print AZB
console.info(incrementString('AZ')); // will print BA
console.info(incrementString('AZZ')); // will print BAA
console.info(incrementString('ABZZ')); // will print ACAA
console.info(incrementString('BA')); // will print BB
console.info(incrementString('BAB')); // will print BAC
// ... and so on ...
回答8:
This one does work well:
var nextLetter = letter => {
let charCode = letter.charCodeAt(0);
let isCapital = letter == letter.toUpperCase();
if (isCapital == true) {
return String.fromCharCode((charCode - 64) % 26 + 65)
} else {
return String.fromCharCode((charCode - 96) % 26 + 97)
}
}
EXAMPLES
nextLetter("a"); // returns 'b'
nextLetter("z"); // returns 'a'
nextLetter("A"); // returns 'B'
nextLetter("Z"); // returns 'A'
回答9:
A just for laughs solution
function nextLetter(str) {
const Alphabet = [
// lower case alphabet
"a", "b", "c",
"d", "e", "f",
"g", "h", "i",
"j", "k", "l",
"m", "n", "o",
"p", "q", "r",
"s", "t", "u",
"v", "w", "x",
"y", "z",
// upper case alphabet
"A", "B", "C",
"D", "E", "F",
"G", "H", "I",
"J", "K", "L",
"M", "N", "O",
"P", "Q", "R",
"S", "T", "U",
"V", "W", "X",
"Y", "Z"
];
const LetterArray = str.split("").map(letter => {
if (Alphabet.includes(letter) === true) {
return Alphabet[Alphabet.indexOf(letter) + 1];
} else {
return " ";
}
});
const Assemble = () => LetterArray.join("").trim();
return Assemble();
}
console.log(nextLetter("hello*3"));回答10:
This is really old. But I needed this functionality and none of the solutions are optimal for my use case. I wanted to generate a, b, c...z, aa,ab...zz, aaa... . This simple recursion does the job.
function nextChar(str) {
if (str.length == 0) {
return 'a';
}
var charA = str.split('');
if (charA[charA.length - 1] === 'z') {
return nextID(str.substring(0, charA.length - 1)) + 'a';
} else {
return str.substring(0, charA.length - 1) +
String.fromCharCode(charA[charA.length - 1].charCodeAt(0) + 1);
}
};
回答11:
Make a function with {a: 'b', b: 'c', etc} in a closure:-
let nextChar = (s => (
"abcdefghijklmopqrstuvwxyza".split('')
.reduce((a,b)=> (s[a]=b, b)), // make the lookup
c=> s[c] // the function returned
))({}); // parameter s, starts empty
usage:-
nextChar('a')
Adding uppercase and digits:-
let nextCh = (
(alphabeta, s) => (
[alphabeta, alphabeta.toUpperCase(), "01234567890"]
.forEach(chars => chars.split('')
.reduce((a,b) => (s[a]=b, b))),
c=> s[c]
)
)("abcdefghijklmopqrstuvwxyza", {});
p.s. In some versions of Javascript, you can use [...chars] instead of chars.split('')
回答12:
Here is a variation of the rot13 algorithm I submitted on https://stackoverflow.com/a/28490254/881441:
function rot1(s) {
return s.replace(/[A-Z]/gi, c =>
"BCDEFGHIJKLMNOPQRSTUVWXYZAbcdefghijklmnopqrstuvwxyza"[
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz".indexOf(c) ] )
}
The input code in the bottom and the looked up codec is on the top (i.e. the output code is the same as the input code but shifted by 1). The function only changes letters, i.e. if any other character is passed in, it will be unchanged by this codec.
来源：https://stackoverflow.com/questions/12504042/what-is-a-method-that-can-be-used-to-increment-letters