sebastienros.jint/Jint/Runtime/Interpreter/Expressions/NullishCoalescingExpression.cs

using System.Runtime.CompilerServices;
using Jint.Native;

namespace Jint.Runtime.Interpreter.Expressions;

internal sealed class NullishCoalescingExpression : JintExpression
{
    private readonly JintExpression _left;
    private readonly JintExpression? _right;
    private readonly JsValue? _constant;

    public NullishCoalescingExpression(LogicalExpression expression) : base(expression)
    {
        _left = Build(expression.Left);

        // we can create a fast path for common literal case like variable ?? 0
        if (expression.Right is Literal l)
        {
            _constant = JintLiteralExpression.ConvertToJsValue(l);
        }
        else
        {
            _right = Build(expression.Right);
        }
    }

    public override JsValue GetValue(EvaluationContext context)
    {
        // need to notify correct node when taking shortcut
        context.LastSyntaxElement = _expression;
        return EvaluateConstantOrExpression(context);
    }

    protected override object EvaluateInternal(EvaluationContext context)
    {
        return EvaluateConstantOrExpression(context);
    }

    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    private JsValue EvaluateConstantOrExpression(EvaluationContext context)
    {
        var left = _left.GetValue(context);

        return !left.IsNullOrUndefined()
            ? left
            : _constant ?? _right!.GetValue(context);
    }
}