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What I want is something like Array.join(separator), but which takes a second argument Array.join(separator, beforeLastElement), so when I say [foo, bar, baz].join(", ", " or") I would get "foo, bar or baz". I guess I could write a function that used Array.slice to separate out the last element, but is there some well known method that I could use instead?
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Use the Array. slice() method to remove the last element from an array, e.g. const withoutLast = arr. slice(0, -1); . The slice method will return a copy of the original array excluding the last element.
The join() method creates and returns a new string by concatenating all of the elements in an array (or an array-like object), separated by commas or a specified separator string. If the array has only one item, then that item will be returned without using the separator.
To get the second to last element in an array, call the at() method on the array, passing it -2 as a parameter, e.g. arr.at(-2) . The at method returns the array element at the specified index. When passed a negative index, the at() method counts back from the last item in the array.
The pop() method removes the last element from an array and returns that element.
May I suggest:
['tom', 'dick', 'harry'].join(', ').replace(/, ([^,]*)$/, ' and $1') > "tom, dick and harry" There's no predefined function, because it's quite simple.
var a = ['a', 'b', 'c']; var str = a.slice(0, -1).join(',')+' or '+a.slice(-1); There's also a specification problem for the main use case of such a function which is natural language formatting. For example if we were to use the Oxford comma logic we would have a different result than what you're looking for:
// 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(", "); } So it seems better to let this problem in userland.
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