# arrayview2iterator > Create an iterator from an array-like object view.
## Usage ```javascript var arrayview2iterator = require( '@stdlib/array/to-view-iterator' ); ``` #### arrayview2iterator( src\[, begin\[, end]]\[, mapFcn\[, thisArg]] ) Returns an iterator which iterates over each element in an array-like `object` view. ```javascript var it = arrayview2iterator( [ 1, 2, 3, 4 ] ); // returns var v = it.next().value; // returns 1 v = it.next().value; // returns 2 v = it.next().value; // returns 3 // ... ``` The returned iterator protocol-compliant object has the following properties: - **next**: function which returns an iterator protocol-compliant object containing the next iterated value (if one exists) assigned to a `value` property and a `done` property having a `boolean` value indicating whether the iterator is finished. - **return**: function which closes an iterator and returns a single (optional) argument in an iterator protocol-compliant object. By default, the returned iterator begins iterating from the first element in an array-like `object`. To specify an alternative starting index, provide a `begin` argument (inclusive). ```javascript var it = arrayview2iterator( [ 1, 2, 3, 4 ], 1 ); // returns var v = it.next().value; // returns 2 v = it.next().value; // returns 3 v = it.next().value; // returns 4 var bool = it.next().done; // returns true ``` If `begin` is less than `0`, the starting index is resolved relative to the last element. For example, the following generates the same behavior as in the previous example ```javascript var it = arrayview2iterator( [ 1, 2, 3, 4 ], -3 ); // returns var v = it.next().value; // returns 2 v = it.next().value; // returns 3 v = it.next().value; // returns 4 var bool = it.next().done; // returns true ``` By default, the returned iterator iterates until the last element in an array-like `object`. To specify an alternative ending index, provide an `end` argument (non-inclusive). ```javascript var it = arrayview2iterator( [ 1, 2, 3, 4 ], 0, 3 ); // returns var v = it.next().value; // returns 1 v = it.next().value; // returns 2 v = it.next().value; // returns 3 var bool = it.next().done; // returns true ``` If `end` is less than `0`, the ending index is resolved relative to the last element. For example, the following generates the same behavior as in the previous example ```javascript var it = arrayview2iterator( [ 1, 2, 3, 4 ], 0, -1 ); // returns var v = it.next().value; // returns 1 v = it.next().value; // returns 2 v = it.next().value; // returns 3 var bool = it.next().done; // returns true ``` To invoke a function for each `src` value, provide a callback function. ```javascript function fcn( v ) { return v * 10.0; } var it = arrayview2iterator( [ 1, 2, 3, 4 ], fcn ); // returns var v = it.next().value; // returns 10.0 v = it.next().value; // returns 20.0 v = it.next().value; // returns 30.0 // ... ``` The invoked function is provided four arguments: - `value`: iterated value - `index`: iterated value index - `n`: iteration count (zero-based) - `src`: source array-like object ```javascript function fcn( v, i ) { return v * (i+1); } var it = arrayview2iterator( [ 1, 2, 3, 4 ], fcn ); // returns var v = it.next().value; // returns 1 v = it.next().value; // returns 4 v = it.next().value; // returns 9 // ... ``` To set the callback function execution context, provide a `thisArg`. ```javascript function fcn( v ) { this.count += 1; return v * 10.0; } var ctx = { 'count': 0 }; var it = arrayview2iterator( [ 1, 2, 3, 4 ], fcn, ctx ); // returns var v = it.next().value; // returns 10.0 v = it.next().value; // returns 20.0 v = it.next().value; // returns 30.0 var count = ctx.count; // returns 3 ```
## Notes - If an environment supports `Symbol.iterator`, the returned iterator is iterable. - If provided a generic `array`, the returned iterator does **not** ignore holes. To achieve greater performance for sparse arrays, use a custom iterator. - A returned iterator does **not** copy a provided array-like `object`. To ensure iterable reproducibility, copy a provided array-like `object` **before** creating an iterator. Otherwise, any changes to the contents of an array-like `object` will be reflected in the returned iterator. - In environments supporting `Symbol.iterator`, the function **explicitly** does **not** invoke an array's `@@iterator` method, regardless of whether this method is defined. To convert an array to an implementation defined iterator, invoke this method directly.
## Examples ```javascript var Float64Array = require( '@stdlib/array/float64' ); var inmap = require( '@stdlib/utils/inmap' ); var randu = require( '@stdlib/random/base/randu' ); var arrayview2iterator = require( '@stdlib/array/to-view-iterator' ); function scale( v, i ) { return v * (i+1); } // Create an array filled with random numbers: var arr = inmap( new Float64Array( 100 ), randu ); // Create an iterator from an array view which scales iterated values: var it = arrayview2iterator( arr, 40, 60, scale ); // Perform manual iteration... var v; while ( true ) { v = it.next(); if ( v.done ) { break; } console.log( v.value ); } ```