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join_to_string.ts
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join_to_string.ts
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// Copyright 2018-2022 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.
/**
* Options for joinToString
*/
export type JoinToStringOptions = {
separator?: string;
prefix?: string;
suffix?: string;
limit?: number;
truncated?: string;
};
/**
* Transforms the elements in the given array to strings using the given
* selector. Joins the produced strings into one using the given `separator`
* and applying the given `prefix` and `suffix` to the whole string afterwards.
* If the array could be huge, you can specify a non-negative value of `limit`,
* in which case only the first `limit` elements will be appended, followed by
* the `truncated` string. Returns the resulting string.
*
* @example
* ```ts
* import { joinToString } from "https://deno.land/std@$STD_VERSION/collections/join_to_string.ts";
* import { assertEquals } from "https://deno.land/std@$STD_VERSION/testing/asserts.ts";
*
* const users = [
* { name: "Kim" },
* { name: "Anna" },
* { name: "Tim" },
* ];
*
* const message = joinToString(users, (it) => it.name, {
* suffix: " are winners",
* prefix: "result: ",
* separator: " and ",
* limit: 1,
* truncated: "others",
* });
*
* assertEquals(message, "result: Kim and others are winners");
* ```
*/
export function joinToString<T>(
array: readonly T[],
selector: (el: T) => string,
{
separator = ",",
prefix = "",
suffix = "",
limit = -1,
truncated = "...",
}: Readonly<JoinToStringOptions> = {},
): string {
let result = "";
let index = -1;
while (++index < array.length) {
const el = array[index];
if (index > 0) {
result += separator;
}
if (limit > -1 && index >= limit) {
result += truncated;
break;
}
result += selector(el);
}
result = prefix + result + suffix;
return result;
}