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* @license Apache-2.0
*
* Copyright (c) 2018 The Stdlib Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
'use strict';
// MODULES //
var isString = require( '@stdlib/assert/is-string' ).isPrimitive;
var isStringArray = require( '@stdlib/assert/is-string-array' ).primitives;
var hasOwnProp = require( '@stdlib/assert/has-own-property' );
var format = require( '@stdlib/string/format' );
// MAIN //
/**
* Returns a partial object copy containing only specified keys. If a key does not exist as an own property in a source object, the key is ignored.
*
* @param {Object} obj - source object
* @param {(string|StringArray)} keys - keys to copy
* @throws {TypeError} first argument must be an object
* @throws {TypeError} second argument must be either a string or an array of strings
* @returns {Object} new object
*
* @example
* var obj1 = {
* 'a': 1,
* 'b': 2
* };
*
* var obj2 = pick( obj1, 'b' );
* // returns { 'b': 2 }
*/
function pick( obj, keys ) {
var out;
var key;
var i;
if ( typeof obj !== 'object' || obj === null ) {
throw new TypeError( format( 'invalid argument. First argument must be an object. Value: `%s`.', obj ) );
}
out = {};
if ( isString( keys ) ) {
if ( hasOwnProp( obj, keys ) ) {
out[ keys ] = obj[ keys ];
}
return out;
}
if ( isStringArray( keys ) ) {
for ( i = 0; i < keys.length; i++ ) {
key = keys[ i ];
if ( hasOwnProp( obj, key ) ) {
out[ key ] = obj[ key ];
}
}
return out;
}
throw new TypeError( format( 'invalid argument. Second argument must be either a string or an array of strings. Value: `%s`.', keys ) );
}
// EXPORTS //
module.exports = pick;
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