feat: add string startsWith method (#514)

Adds startsWith method to the String builtins.

builtin_string.go

@@ -443,6 +443,17 @@ func builtinStringSubstr(call FunctionCall) Value {
 	return stringValue(string(target[start : start+length]))
 }
 
+func builtinStringStartsWith(call FunctionCall) Value {
+	checkObjectCoercible(call.runtime, call.This)
+	target := call.This.string()
+	search := call.Argument(0).string()
+	length := len(search)
+	if length > len(target) {
+		return boolValue(false)
+	}
+	return boolValue(target[:length] == search)
+}
+
 func builtinStringToLowerCase(call FunctionCall) Value {
 	checkObjectCoercible(call.runtime, call.This)
 	return stringValue(strings.ToLower(call.This.string()))

inline_test.go

@@ -102,7 +102,7 @@ func TestGetOwnPropertyNames(t *testing.T) {
 			"substr",
 			"substring",
 			// "sup",
-			// "startsWith",
+			"startsWith",
 			"toString",
 			"trim",
 			// "trimStart",

string_test.go

@@ -470,3 +470,12 @@ func TestString_localeCompare(t *testing.T) {
 		test(`'a'.localeCompare('a');`, 0)
 	})
 }
+
+func TestString_startsWith(t *testing.T) {
+	tt(t, func() {
+		test, _ := test()
+
+		test(`'a'.startsWith('c');`, false)
+		test(`'aa'.startsWith('a');`, true)
+	})
+}

tools/gen-jscore/.gen-jscore.yaml

@@ -184,6 +184,8 @@ types:
           function: 2
         - name: substring
           function: 2
+        - name: startsWith
+          function: 1
         - name: toString
           function: -1
         - name: trim