refactor: clean-up dtype validation logic

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---

Author: kgryte

lib/node_modules/@stdlib/array/nans-like/lib/main.js

@@ -20,18 +20,22 @@
 
 // MODULES //
 
+var contains = require( '@stdlib/array/base/assert/contains' ).factory;
 var dtype = require( '@stdlib/array/dtype' );
 var full = require( '@stdlib/array/full' );
 var Complex128 = require( '@stdlib/complex/float64/ctor' );
 var Complex64 = require( '@stdlib/complex/float32/ctor' );
+var dtypes = require( '@stdlib/array/dtypes' );
+var join = require( '@stdlib/array/base/join' );
 var format = require( '@stdlib/string/format' );
 
 
 // VARIABLES //
 
 var Z128 = new Complex128( NaN, NaN );
 var Z64 = new Complex64( NaN, NaN );
-var DTYPES = [ 'float64', 'float32', 'complex128', 'complex64', 'generic' ];
+var DTYPES = dtypes( 'floating_point_and_generic' );
+var isValidDType = contains( DTYPES );
 
 
 // MAIN //
@@ -63,11 +67,11 @@ function nansLike( x ) {
 	}
 	if ( arguments.length > 1 ) {
 		dt = arguments[ 1 ];
-		if ( DTYPES.indexOf( dt ) === -1 ) {
-			throw new TypeError( format( 'invalid argument. Second argument must be one of the following: "%s". Value: `%s`.', DTYPES.join( '", "' ), dt ) );
+		if ( !isValidDType( dt ) ) {
+			throw new TypeError( format( 'invalid argument. Second argument must be one of the following: "%s". Value: `%s`.', join( DTYPES, '", "' ), dt ) );
 		}
-	} else if ( DTYPES.indexOf( dt ) === -1 ) {
-		throw new TypeError( format( 'invalid argument. First argument must be one of the following data types: "%s". Value: `%s`.', DTYPES.join( '", "' ), dt ) );
+	} else if ( !isValidDType( dt ) ) {
+		throw new TypeError( format( 'invalid argument. First argument must have one of the following data types: "%s". Value: `%s`.', join( DTYPES, '", "' ), dt ) );
 	}
 	if ( dt === 'complex128' ) {
 		v = Z128;