Fix the type of copyWithin

Only the first parameter of `copyWithin` is required, contrary to the type in the typedef. This commit fixes that type to allow correct usage of the `copyWithin`
function. See [the usage of copy within](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/copyWithin).

Author: ericbf

src/lib/es2015.core.d.ts

@@ -33,15 +33,23 @@ interface Array<T> {
     fill(value: T, start?: number, end?: number): this;
 
     /**
-     * Returns the this object after copying a section of the array identified by start and end
-     * to the same array starting at position target
-     * @param target If target is negative, it is treated as length+target where length is the
-     * length of the array.
-     * @param start If start is negative, it is treated as length+start. If end is negative, it
-     * is treated as length+end.
-     * @param end If not specified, length of the this object is used as its default value.
-     */
-    copyWithin(target: number, start: number, end?: number): this;
+     * Return the `this` object after shallow copying part of the array to another location in the same array, without modifying its length.
+     * @param target Zero-based index at which to copy the sequence to, converted to an integer.
+     * - Negative index counts back from the end of the array — if `target < 0`, `target + array.length` is used.
+     * - If `target < -array.length`, `0` is used.
+     * - If `target >= array.length`, nothing is copied.
+     * - If `target` is positioned after `start` after normalization, copying only happens until the end of `array.length` (in other words, `copyWithin()` never extends the array).
+     * @param start Zero-based index at which to start copying elements from, converted to an integer.
+     * - Negative index counts back from the end of the array — if `start < 0`, `start + array.length` is used.
+     * - If `start < -array.length` or `start` is omitted, `0` is used.
+     * - If `start >= array.length`, nothing is copied.
+     * @param end Zero-based index at which to end copying elements from, converted to an integer. `copyWithin()` copies up to but not including end.
+     * - Negative index counts back from the end of the array — if `end < 0`, `end + array.length` is used.
+     * - If `end < -array.length`, `0` is used.
+     * - If `end >= array.length` or `end` is omitted, `array.length` is used, causing all elements until the end to be copied.
+     * - If `end` is positioned before or at `start` after normalization, nothing is copied.
+     */
+    copyWithin(target: number, start?: number, end?: number): this;
 }
 
 interface ArrayConstructor {

src/lib/es2020.bigint.d.ts

@@ -142,15 +142,23 @@ interface BigInt64Array {
     readonly byteOffset: number;
 
     /**
-     * Returns the this object after copying a section of the array identified by start and end
-     * to the same array starting at position target
-     * @param target If target is negative, it is treated as length+target where length is the
-     * length of the array.
-     * @param start If start is negative, it is treated as length+start. If end is negative, it
-     * is treated as length+end.
-     * @param end If not specified, length of the this object is used as its default value.
-     */
-    copyWithin(target: number, start: number, end?: number): this;
+     * Return the `this` object after shallow copying part of the array to another location in the same array, without modifying its length.
+     * @param target Zero-based index at which to copy the sequence to, converted to an integer.
+     * - Negative index counts back from the end of the array — if `target < 0`, `target + array.length` is used.
+     * - If `target < -array.length`, `0` is used.
+     * - If `target >= array.length`, nothing is copied.
+     * - If `target` is positioned after `start` after normalization, copying only happens until the end of `array.length` (in other words, `copyWithin()` never extends the array).
+     * @param start Zero-based index at which to start copying elements from, converted to an integer.
+     * - Negative index counts back from the end of the array — if `start < 0`, `start + array.length` is used.
+     * - If `start < -array.length` or `start` is omitted, `0` is used.
+     * - If `start >= array.length`, nothing is copied.
+     * @param end Zero-based index at which to end copying elements from, converted to an integer. `copyWithin()` copies up to but not including end.
+     * - Negative index counts back from the end of the array — if `end < 0`, `end + array.length` is used.
+     * - If `end < -array.length`, `0` is used.
+     * - If `end >= array.length` or `end` is omitted, `array.length` is used, causing all elements until the end to be copied.
+     * - If `end` is positioned before or at `start` after normalization, nothing is copied.
+     */
+    copyWithin(target: number, start?: number, end?: number): this;
 
     /** Yields index, value pairs for every entry in the array. */
     entries(): IterableIterator<[number, bigint]>;
@@ -414,15 +422,23 @@ interface BigUint64Array {
     readonly byteOffset: number;
 
     /**
-     * Returns the this object after copying a section of the array identified by start and end
-     * to the same array starting at position target
-     * @param target If target is negative, it is treated as length+target where length is the
-     * length of the array.
-     * @param start If start is negative, it is treated as length+start. If end is negative, it
-     * is treated as length+end.
-     * @param end If not specified, length of the this object is used as its default value.
-     */
-    copyWithin(target: number, start: number, end?: number): this;
+     * Return the `this` object after shallow copying part of the array to another location in the same array, without modifying its length.
+     * @param target Zero-based index at which to copy the sequence to, converted to an integer.
+     * - Negative index counts back from the end of the array — if `target < 0`, `target + array.length` is used.
+     * - If `target < -array.length`, `0` is used.
+     * - If `target >= array.length`, nothing is copied.
+     * - If `target` is positioned after `start` after normalization, copying only happens until the end of `array.length` (in other words, `copyWithin()` never extends the array).
+     * @param start Zero-based index at which to start copying elements from, converted to an integer.
+     * - Negative index counts back from the end of the array — if `start < 0`, `start + array.length` is used.
+     * - If `start < -array.length` or `start` is omitted, `0` is used.
+     * - If `start >= array.length`, nothing is copied.
+     * @param end Zero-based index at which to end copying elements from, converted to an integer. `copyWithin()` copies up to but not including end.
+     * - Negative index counts back from the end of the array — if `end < 0`, `end + array.length` is used.
+     * - If `end < -array.length`, `0` is used.
+     * - If `end >= array.length` or `end` is omitted, `array.length` is used, causing all elements until the end to be copied.
+     * - If `end` is positioned before or at `start` after normalization, nothing is copied.
+     */
+    copyWithin(target: number, start?: number, end?: number): this;
 
     /** Yields index, value pairs for every entry in the array. */
     entries(): IterableIterator<[number, bigint]>;