有没有办法连接js数组中的元素，但让最后一个分隔符不同？

Question

我想要的是像Array.join(separator)，但它需要第二个参数Array.join(separator, beforeLastElement)，所以当我说[foo, bar, baz].join(", ", " or")我会得到"foo, bar or baz"。我想我可以编写一个使用Array.slice来分离最后一个元素的函数，但是有一些我可以使用的众所周知的方法吗？

Answer 1

不，这很具体，你必须编写一个自定义函数。好消息是，正如你所说，一旦你使用Array.join来处理所有的分隔符，最后一个将很容易更新。

Answer 2

使用reduce功能的在线解决方案：

[1, 2, 3, 4, 5].reduce((text, value, i) => !i ? value : `${text}, ${value}`, '');

==> "1, 2, 3, 4, 5"

Answer 3

没有预定义的功能，因为它非常简单。

var a = ['a', 'b', 'c'];
var str = a.slice(0, -1).join(',')+' or '+a.slice(-1);

对于这种功能的主要用例，还存在规范问题，即自然语言格式化。例如，如果我们使用牛津逗号逻辑，我们将得到与您正在寻找的结果不同的结果：

// make a list in the Oxford comma style (eg "a, b, c, and d")
// Examples with conjunction "and":
// ["a"] -> "a"
// ["a", "b"] -> "a and b"
// ["a", "b", "c"] -> "a, b, and c"
exports.oxford = function(arr, conjunction, ifempty){
    let l = arr.length;
    if (!l) return ifempty;
    if (l<2) return arr[0];
    if (l<3) return arr.join(` ${conjunction} `);
    arr = arr.slice();
    arr[l-1] = `${conjunction} ${arr[l-1]}`;
    return arr.join(", ");
}

所以在userland中让这个问题似乎更好。

Answer 4

我可以建议：

['tom', 'dick', 'harry'].join(', ').replace(/, ([^,]*)$/, ' and $1')
> "tom, dick and harry"

Answer 5

建立@ dystroy的答案：

function formatArray(arr){
    var outStr = "";
    if (arr.length === 1) {
        outStr = arr[0];
    } else if (arr.length === 2) {
        //joins all with "and" but no commas
        //example: "bob and sam"
        outStr = arr.join(' and ');
    } else if (arr.length > 2) {
        //joins all with commas, but last one gets ", and" (oxford comma!)
        //example: "bob, joe, and sam"
        outStr = arr.slice(0, -1).join(', ') + ', and ' + arr.slice(-1);
    }
    return outStr;
}

示例用法：

formatArray([]);                //""
formatArray(["a"]);             //"a"
formatArray(["a","b"]);         //"a and b"
formatArray(["a","b","c"]);     //"a, b, and c"
formatArray(["a","b","c","d"]); //"a, b, c, and d"

Answer 6

Array.prototype.join2 = function(all, last) {
    var arr = this.slice();                   //make a copy so we don't mess with the original
    var lastItem = arr.splice(-1);            //strip out the last element
    arr = arr.length ? [arr.join(all)] : [];  //make an array with the non-last elements joined with our 'all' string, or make an empty array
    arr.push(lastItem);                       //add last item back so we should have ["some string with first stuff split by 'all'", last item]; or we'll just have [lastItem] if there was only one item, or we'll have [] if there was nothing in the original array
    return arr.join(last);                    //now we join the array with 'last'
}

> [1,2,3,4].join2(', ', ' and ');
>> "1, 2, 3 and 4"

Answer 7

有一个包join-array

const join = require('join-array');
const names = ['Rachel','Taylor','Julia','Robert','Jasmine','Lily','Madison'];
const config = {
  array: names,
  separator: ', ',
  last: ' and ',
  max: 4,
  maxMessage:(missed)=>`(${missed} more...)`
};
const list = join(config); //Rachel, Taylor, Julia, (3 more...) and Madison

Answer 8

紧凑版:)

function customJoin(arr,s1,s2){
return(arr.slice(0,-1).join(s1).concat(arr.length > 1 ? s2 : '', arr.slice(-1)));
}

/* 
arr: data array
s1: regular seperator (string)
s2: last seperator (string)
*/

function customJoin(arr,s1,s2){
return(arr.slice(0,-1).join(s1).concat(arr.length > 1 ? s2 : '', arr.slice(-1)));
}

let arr1 = ['a','b','c','d'];
let arr2 = ['singleToken'];

console.log(customJoin(arr1,',',' and '));
//expected: 'a,b,c and d'
console.log(customJoin(arr1,'::',' and finally::'));
//expected: 'a::b::c and finally::d'
console.log(customJoin(arr2,',','and '));
//expected: 'singleToken'

Answer 9

虽然它是一个迟到的答案，添加一些方法。

方法1：使用Array.splice（）在最后一个元素之前添加last delimiter并加入并删除最后两个,。

function join(arr,last)
{
    if(!Array.isArray(arr)) throw "Passed value is not of array type.";
    last = last || ' and '; //set 'and' as default
    
    (arr.length>1 && arr.splice(-1,0,last));
    arr = arr.join().split("");
    arr[arr.lastIndexOf(",")]="";
    arr[arr.lastIndexOf(",")]="";
    return arr.join("");
}

console.log( join([1]) ); //single valued array
console.log( join([1,2]) ); //double valued array
console.log( join([1,2,3]) ); //more than 2 values array,
console.log( join([1,2,3],' or ') ); //with custom last delimiter
console.log( join("name") ); //Non-array type

方法2：使用Array.reduce（）通过遍历每个元素来构造字符串。

function join(arr,last)
{
    if(!Array.isArray(arr)) throw "Passed value is not of array type.";
    last=last||' and ';
    
    return arr.reduce(function(acc,value,index){
        if(arr.length<2) return arr.join();
        return acc + (index>=arr.length-2 ? index>arr.length-2 ? value : value+last : value+",");
    },"");
}

console.log( join([1]) ); //single valued array
console.log( join([1,2]) ); //double valued array
console.log( join([1,2,3]) ); //more than 2 values array,
console.log( join([1,2,3,4],' or ') ); //with custom last delimiter
console.log( join("name") ); //Non-array type

Answer 10

对我来说，最简单的解决方案是：

['1', '2', '3'].reduce((previous, current, index, array) => {
    if (index === array.length - 1) {
        return previous + ' & ' + current;
    } else {
        return previous + ', ' + current;
    }
})