sebastienros.jint/Jint/Extensions/Polyfills.cs

namespace Jint;

internal static class Polyfills
{
#if NETFRAMEWORK || NETSTANDARD2_0
    [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
    internal static bool Contains(this string source, char c) => source.IndexOf(c) != -1;

    [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
    internal static bool StartsWith(this string source, char c) => source.Length > 0 && source[0] == c;
#endif

#if NETFRAMEWORK
    [System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
    internal static bool Contains(this ReadOnlySpan<string> source, string c) => source.IndexOf(c) != -1;
#endif
}