LibJS: Add String.prototype.{trim, trimStart, trimEnd} (#1792)

Author: https://github.com/kessejones 🔰
Commit: https://github.com/SerenityOS/serenity/commit/994f1a79ad6
Pull-request: https://github.com/SerenityOS/serenity/pull/1792
Reviewed-by: https://github.com/linusg

Libraries/LibJS/Runtime/StringPrototype.cpp

@@ -51,6 +51,10 @@ StringPrototype::StringPrototype()
     put_native_function("toString", to_string, 0);
     put_native_function("padStart", pad_start, 1);
     put_native_function("padEnd", pad_end, 1);
+
+    put_native_function("trim", trim, 0);
+    put_native_function("trimStart", trimStart, 0);
+    put_native_function("trimEnd", trimEnd, 0);
 }
 
 StringPrototype::~StringPrototype()
@@ -235,4 +239,70 @@ Value StringPrototype::pad_end(Interpreter& interpreter)
     return pad_string(interpreter, this_object, PadPlacement::End);
 }
 
+enum class TrimMode {
+    Left,
+    Right,
+    Both
+};
+
+static Value trim_string(Interpreter& interpreter, Object* object, TrimMode mode)
+{
+    auto& string = object->to_string().as_string()->string();
+
+    size_t substring_start = 0;
+    size_t substring_length = string.length();
+
+    auto is_white_space_character = [](char character) -> bool {
+        return character == 0x9 || character == 0xa || character == 0xb || character == 0xc || character == 0xd || character == 0x20;
+    };
+
+    if (mode == TrimMode::Left || mode == TrimMode::Both) {
+        for (size_t i = 0; i < string.length(); ++i) {
+            if (!is_white_space_character(string.characters()[i])) {
+                substring_start = i;
+                substring_length -= substring_start;
+                break;
+            }
+        }
+    }
+
+    if (substring_length == 0)
+        return js_string(interpreter, String());
+
+    if (mode == TrimMode::Right || mode == TrimMode::Both) {
+        size_t count = 0;
+        for (size_t i = string.length() - 1; i > 0; --i) {
+            if (!is_white_space_character(string.characters()[i])) {
+                substring_length -= count;
+                break;
+            }
+            count++;
+        }
+    }
+
+    auto substring = string.substring(substring_start, substring_length);
+    return js_string(interpreter, substring);
+}
+
+Value StringPrototype::trim(Interpreter& interpreter)
+{
+    auto* this_object = interpreter.this_value().to_object(interpreter.heap());
+
+    return trim_string(interpreter, this_object, TrimMode::Both);
+}
+
+Value StringPrototype::trimStart(Interpreter& interpreter)
+{
+    auto* this_object = interpreter.this_value().to_object(interpreter.heap());
+
+    return trim_string(interpreter, this_object, TrimMode::Left);
+}
+
+Value StringPrototype::trimEnd(Interpreter& interpreter)
+{
+    auto* this_object = interpreter.this_value().to_object(interpreter.heap());
+
+    return trim_string(interpreter, this_object, TrimMode::Right);
+}
+
 }

Libraries/LibJS/Runtime/StringPrototype.h

@@ -49,6 +49,10 @@ private:
     static Value pad_end(Interpreter&);
 
     static Value length_getter(Interpreter&);
+
+    static Value trim(Interpreter&);
+    static Value trimStart(Interpreter&);
+    static Value trimEnd(Interpreter&);
 };
 
 }

Libraries/LibJS/Tests/String.prototype.trim.js

@@ -0,0 +1,56 @@
+load("test-common.js");
+
+try {
+    assert(String.prototype.trim.length === 0);
+    assert(String.prototype.trimStart.length === 0);
+    assert(String.prototype.trimEnd.length === 0);
+    assert("   hello friends  ".trim() === "hello friends");
+    assert("hello friends   ".trim() === "hello friends");
+    assert("   hello friends".trim() === "hello friends");
+    assert("   hello friends".trimStart() === "hello friends");
+    assert("hello friends   ".trimEnd() === "hello friends");
+    assert("   hello friends".trimEnd() === "   hello friends");
+    assert("hello friends   ".trimStart() === "hello friends   ");
+    assert("   hello friends   ".trimEnd() === "   hello friends");
+    assert("    hello friends   ".trimStart() === "hello friends   ");
+
+    assert("\thello friends".trimStart() === "hello friends");
+    assert("hello friends\t".trimStart() === "hello friends\t");
+    assert("\thello friends\t".trimStart() === "hello friends\t");
+    
+    assert("\rhello friends".trimStart() === "hello friends");
+    assert("hello friends\r".trimStart() === "hello friends\r");
+    assert("\rhello friends\r".trimStart() === "hello friends\r");
+
+    assert("hello friends\t".trimEnd() === "hello friends");
+    assert("\thello friends".trimEnd() === "\thello friends");
+    assert("\thello friends\t".trimEnd() === "\thello friends");
+    
+    assert("hello friends\r".trimEnd() === "hello friends");
+    assert("\rhello friends".trimEnd() === "\rhello friends");
+    assert("\rhello friends\r".trimEnd() === "\rhello friends");
+    
+    assert("hello friends\n".trimEnd() === "hello friends");
+    assert("\r\nhello friends".trimEnd() === "\r\nhello friends");
+    assert("\rhello friends\r\n".trimEnd() === "\rhello friends");
+
+    assert("\thello friends\t".trim() === "hello friends");
+    assert("\thello friends".trim() === "hello friends");
+    assert("hello friends\t".trim() === "hello friends");
+    
+    assert("\rhello friends\r".trim() === "hello friends");
+    assert("\rhello friends".trim() === "hello friends");
+    assert("hello friends\r".trim() === "hello friends");
+    
+    assert("\rhello friends\n".trim() === "hello friends");
+    assert("\r\thello friends".trim() === "hello friends");
+    assert("hello friends\r\n".trim() === "hello friends");
+    assert("  \thello friends\r\n".trim() === "hello friends");
+    assert("\n\t\thello friends\r\n".trim() === "hello friends");
+    assert("\n\t\thello friends\t\t".trim() === "hello friends");
+
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}