WordPress at a glance
function is not described

wp_get_script_polyfill() WP 5.0.0

Returns contents of an inline script used in appending polyfill scripts for browsers which fail the provided tests. The provided array is a mapping from a condition to verify feature support to its polyfill script handle.

Hooks in function
Return

String. Conditional polyfill inline script.

Usage

wp_get_script_polyfill( &$scripts, $tests );
$scripts(WP_Scripts) (required)
WP_Scripts object.
$tests(array) (required)
Features to detect.

Code of wp get script polyfill: wp-includes/script-loader.php VER 5.0.3

<?php
function wp_get_script_polyfill( &$scripts, $tests ) {
	$polyfill = '';
	foreach ( $tests as $test => $handle ) {
		if ( ! array_key_exists( $handle, $scripts->registered ) ) {
			continue;
		}

		$src = $scripts->registered[ $handle ]->src;
		$ver = $scripts->registered[ $handle ]->ver;

		if ( ! preg_match( '|^(https?:)?//|', $src ) && ! ( $scripts->content_url && 0 === strpos( $src, $scripts->content_url ) ) ) {
			$src = $scripts->base_url . $src;
		}

		if ( ! empty( $ver ) ) {
			$src = add_query_arg( 'ver', $ver, $src );
		}

		/** This filter is documented in wp-includes/class.wp-scripts.php */
		$src = esc_url( apply_filters( 'script_loader_src', $src, $handle ) );

		if ( ! $src ) {
			continue;
		}

		$polyfill .= (
			// Test presence of feature...
			'( ' . $test . ' ) || ' .
			// ...appending polyfill on any failures. Cautious viewers may balk
			// at the `document.write`. Its caveat of synchronous mid-stream
			// blocking write is exactly the behavior we need though.
			'document.write( \'<script src="' .
			$src .
			'"></scr\' + \'ipt>\' );'
		);
	}

	return $polyfill;
}