If without else

src/compiler.js

@@ -31,7 +31,7 @@ module.exports = compile;
 
 const parser = require("../parser/jaz.js").parser;
 
-const timeout = ms => new Promise(res => setTimeout(res, ms))
+const timeout = ms => new Promise(res => setTimeout(res, ms));
 
 async function compile(srcFile) {
     const fullFileName = srcFile;

src/exec.js

@@ -578,8 +578,10 @@ function execIf(ctx, ast) {
         exec(ctx, ast.then);
         if (ctx.error) return;
     } else {
-        exec(ctx, ast.else);
-        if (ctx.error) return;
+        if (ast.else) {
+            exec(ctx, ast.else);
+            if (ctx.error) return;
+        }
     }
 }
 

src/gencode.js

@@ -246,9 +246,13 @@ function genIf(ctx, ast) {
     if (ctx.error) return;
     const thenBody = gen(ctx, ast.then);
     if (ctx.error) return;
-    const elseBody = gen(ctx, ast.else);
-    if (ctx.error) return;
-    return `if (${condition}) {\n${thenBody}\n} else {\n${elseBody}\n}\n`;
+    if (ast.else) {
+        const elseBody = gen(ctx, ast.else);
+        if (ctx.error) return;
+        return `if (${condition}) {\n${thenBody}\n} else {\n${elseBody}\n}\n`;
+    } else {
+        return `if (${condition}) {\n${thenBody}\n}\n`;
+    }
 }