97 lines
2.0 KiB
JavaScript
97 lines
2.0 KiB
JavaScript
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/**
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* @license Apache-2.0
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*
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* Copyright (c) 2018 The Stdlib Authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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'use strict';
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// MODULES //
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var isFunction = require( '@stdlib/assert/is-function' );
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// MAIN //
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/**
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* Function composition.
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*
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* @param {...Function} f - functions to compose
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* @throws {Error} must provide more than one argument
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* @throws {TypeError} must provide functions
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* @returns {Function} composite function
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*
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* @example
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* function a( x ) {
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* return 2 * x;
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* }
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*
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* function b( x ) {
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* return x + 3;
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* }
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*
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* function c( x ) {
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* return x / 5;
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* }
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*
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* var f = compose( c, b, a );
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*
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* var z = f( 6 );
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* // returns 3
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*/
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function compose() {
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var nFuncs;
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var f;
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var i;
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nFuncs = arguments.length;
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if ( nFuncs < 2 ) {
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throw new Error( 'insufficient input arguments. Must provide multiple functions to compose.' );
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}
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f = new Array( nFuncs );
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for ( i = 0; i < nFuncs; i++ ) {
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f[ i ] = arguments[ i ];
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if ( !isFunction( f[ i ] ) ) {
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throw new TypeError( 'invalid argument. All arguments must be functions. Value: `'+f[ i ]+'`.' );
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}
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}
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return composite;
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/**
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* Composite function.
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*
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* @private
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* @param {...*} args - arguments
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* @returns {*} result
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*/
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function composite() {
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var args;
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var i;
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args = new Array( arguments.length );
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for ( i = 0; i < args.length; i++ ) {
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args[ i ] = arguments[ i ];
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}
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args = f[ nFuncs-1 ].apply( null, args );
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for ( i = nFuncs-2; i >= 0; i-- ) {
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args = f[ i ]( args );
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}
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return args;
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}
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}
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// EXPORTS //
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module.exports = compose;
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