TypeScriptToLua · Perryvw · May 2, 2019 · May 2, 2019
diff --git a/src/LuaLib.ts b/src/LuaLib.ts
@@ -39,9 +39,11 @@ export enum LuaLibFeature {
     WeakMap = "WeakMap",
     WeakSet = "WeakSet",
     SourceMapTraceBack = "SourceMapTraceBack",
+    StringConcat = "StringConcat",
+    StringEndsWith = "StringEndsWith",
     StringReplace = "StringReplace",
     StringSplit = "StringSplit",
-    StringConcat = "StringConcat",
+    StringStartsWith = "StringStartsWith",
     Symbol = "Symbol",
     SymbolRegistry = "SymbolRegistry",
 }

diff --git a/src/LuaTransformer.ts b/src/LuaTransformer.ts
@@ -4003,6 +4003,10 @@ export class LuaTransformer {
                 const firstParamPlusOne = this.expressionPlusOne(params[0]);
                 return this.createStringCall("byte", node, caller, firstParamPlusOne);
             }
+            case "startsWith":
+                return this.transformLuaLibFunction(LuaLibFeature.StringStartsWith, node, caller, ...params);
+            case "endsWith":
+                return this.transformLuaLibFunction(LuaLibFeature.StringEndsWith, node, caller, ...params);
             case "byte":
             case "char":
             case "dump":

diff --git a/src/lualib/StringEndsWith.ts b/src/lualib/StringEndsWith.ts
@@ -0,0 +1,7 @@
+function __TS__StringEndsWith(this: string, searchString: string, endPosition?: number): boolean {
+    if (endPosition === undefined || endPosition > this.length) {
+        endPosition = this.length;
+    }
+
+    return string.sub(this, endPosition - searchString.length + 1, endPosition) === searchString;
+}
diff --git a/src/lualib/StringStartsWith.ts b/src/lualib/StringStartsWith.ts
@@ -0,0 +1,7 @@
+function __TS__StringStartsWith(this: string, searchString: string, position?: number): boolean {
+    if (position === undefined || position < 0) {
+        position = 0;
+    }
+
+    return string.sub(this, position + 1, searchString.length + position) === searchString;
+}
diff --git a/src/lualib/declarations/string.d.ts b/src/lualib/declarations/string.d.ts
@@ -9,4 +9,5 @@ declare namespace string {
     function gsub(source: string, searchValue: string, replaceValue: (...groups: string[]) => string): [string, number];
 
     function gmatch(haystack: string, pattern: string): GMatchResult;
+    function sub(s: string, i: number, j?: number): string;
 }
diff --git a/test/unit/string.spec.ts b/test/unit/string.spec.ts
@@ -271,6 +271,30 @@ test.each([
     expect(result).toBe(inp.charAt(index));
 });
 
+test.each<{ inp: string; args: Parameters<string["startsWith"]> }>([
+    { inp: "hello test", args: [""] },
+    { inp: "hello test", args: ["hello"] },
+    { inp: "hello test", args: ["test"] },
+    { inp: "hello test", args: ["test", 6] },
+])("string.startsWith (%p)", ({ inp, args }) => {
+    const argsString = args.map(arg => JSON.stringify(arg)).join(", ");
+    const result = util.transpileAndExecute(`return "${inp}".startsWith(${argsString})`);
+
+    expect(result).toBe(inp.startsWith(...args));
+});
+
+test.each<{ inp: string; args: Parameters<string["endsWith"]> }>([
+    { inp: "hello test", args: [""] },
+    { inp: "hello test", args: ["test"] },
+    { inp: "hello test", args: ["hello"] },
+    { inp: "hello test", args: ["hello", 5] },
+])("string.endsWith (%p)", ({ inp, args }) => {
+    const argsString = args.map(arg => JSON.stringify(arg)).join(", ");
+    const result = util.transpileAndExecute(`return "${inp}".endsWith(${argsString})`);
+
+    expect(result).toBe(inp.endsWith(...args));
+});
+
 test.each([
     { input: "abcd", index: 3 },
     { input: "abcde", index: 3 },