Add array/length (#68)

* Add length method for arrays

* Add tests for length method

* Update questions and add additional question

* Separate some test cases

Co-authored-by: Krystian Boruciński <krystian.borucinski@sandstream.pl>

Author: kborucinski

README.md

@@ -553,6 +553,44 @@ last([]);
 
 - How to get the last element of an array?
 
+#### length
+
+Returns the number of elements in the given array.
+
+##### Type signature
+
+<!-- prettier-ignore-start -->
+```typescript
+(xs: any[]) => number
+```
+<!-- prettier-ignore-end -->
+
+##### Examples
+
+<!-- prettier-ignore-start -->
+```javascript
+length([true, 1]);
+// ⇒ 2
+```
+
+```javascript
+length([1, 2, 3]);
+// ⇒ 3
+```
+
+```javascript
+length([]);
+// ⇒ 0
+```
+<!-- prettier-ignore-end -->
+
+##### Questions
+
+- How to check an array's length?
+- How to compute an array's length?
+- How to check the size of an array?
+- How to check the number of elements in an array?
+
 #### lengthDiffers
 
 Checks if lengths of the given arrays differ.

array/README.md

@@ -536,6 +536,44 @@ last([]);
 
 - How to get the last element of an array?
 
+# length
+
+Returns the number of elements in the given array.
+
+## Type signature
+
+<!-- prettier-ignore-start -->
+```typescript
+(xs: any[]) => number
+```
+<!-- prettier-ignore-end -->
+
+## Examples
+
+<!-- prettier-ignore-start -->
+```javascript
+length([true, 1]);
+// ⇒ 2
+```
+
+```javascript
+length([1, 2, 3]);
+// ⇒ 3
+```
+
+```javascript
+length([]);
+// ⇒ 0
+```
+<!-- prettier-ignore-end -->
+
+## Questions
+
+- How to check an array's length?
+- How to compute an array's length?
+- How to check the size of an array?
+- How to check the number of elements in an array?
+
 # lengthDiffers
 
 Checks if lengths of the given arrays differ.

array/index.js

@@ -16,6 +16,7 @@ import insert from "./insert.js";
 import intersection from "./intersection.js";
 import is from "./is.js";
 import last from "./last.js";
+import length from "./length.js";
 import lengthDiffers from "./lengthDiffers.js";
 import map from "./map.js";
 import midpoint from "./midpoint.js";
@@ -65,6 +66,7 @@ export {
   intersection,
   is,
   last,
+  length,
   lengthDiffers,
   map,
   midpoint,
@@ -115,6 +117,7 @@ export default {
   intersection,
   is,
   last,
+  length,
   lengthDiffers,
   map,
   midpoint,

array/index.ts

@@ -16,6 +16,7 @@ import insert from "./insert";
 import intersection from "./intersection";
 import is from "./is";
 import last from "./last";
+import length from "./length";
 import lengthDiffers from "./lengthDiffers";
 import map from "./map";
 import midpoint from "./midpoint";
@@ -65,6 +66,7 @@ export {
   intersection,
   is,
   last,
+  length,
   lengthDiffers,
   map,
   midpoint,
@@ -115,6 +117,7 @@ export default {
   intersection,
   is,
   last,
+  length,
   lengthDiffers,
   map,
   midpoint,

array/length.js

@@ -0,0 +1 @@
+export default xs => xs.length;

array/length.json

@@ -0,0 +1,25 @@
+{
+  "name": "length",
+  "description": "Returns the number of elements in the given array.",
+  "signature": "(xs: any[]) => number",
+  "examples": [
+    {
+      "language": "javascript",
+      "content": "length([true, 1]);\n// ⇒ 2"
+    },
+    {
+      "language": "javascript",
+      "content": "length([1, 2, 3]);\n// ⇒ 3"
+    },
+    {
+      "language": "javascript",
+      "content": "length([]);\n// ⇒ 0"
+    }
+  ],
+  "questions": [
+    "How to check an array's length?",
+    "How to compute an array's length?",
+    "How to check the size of an array?",
+    "How to check the number of elements in an array?"
+  ]
+}

array/length.md

@@ -0,0 +1,37 @@
+# length
+
+Returns the number of elements in the given array.
+
+## Type signature
+
+<!-- prettier-ignore-start -->
+```typescript
+(xs: any[]) => number
+```
+<!-- prettier-ignore-end -->
+
+## Examples
+
+<!-- prettier-ignore-start -->
+```javascript
+length([true, 1]);
+// ⇒ 2
+```
+
+```javascript
+length([1, 2, 3]);
+// ⇒ 3
+```
+
+```javascript
+length([]);
+// ⇒ 0
+```
+<!-- prettier-ignore-end -->
+
+## Questions
+
+- How to check an array's length?
+- How to compute an array's length?
+- How to check the size of an array?
+- How to check the number of elements in an array?

array/length.test.ts

@@ -0,0 +1,14 @@
+/* eslint-env jest */
+// @ts-ignore ambiguous import
+import length from "./length";
+
+describe("length", () => {
+  it("returns the length of the given array", () => {
+    expect(length([1, 2, 3])).toEqual(3);
+    expect(length([6, 7])).toEqual(2);
+  });
+
+  it("returns zero when the given array is empty", () => {
+    expect(length([])).toEqual(0);
+  });
+});

array/length.ts

@@ -0,0 +1 @@
+export default (xs: any[]): number => xs.length;