Add console.clear() (#1562)

js/console.ts

@@ -1,5 +1,7 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
 import { isTypedArray } from "./util";
+import { TextEncoder } from "./text_encoding";
+import { File, stdout } from "./files";
 
 // tslint:disable-next-line:no-any
 type ConsoleContext = Set<any>;
@@ -23,6 +25,20 @@ const CHAR_LOWERCASE_F = 102; /* f */
 const CHAR_LOWERCASE_O = 111; /* o */
 const CHAR_UPPERCASE_O = 79; /* O */
 const CHAR_LOWERCASE_C = 99; /* c */
+export class CSI {
+  static kClear = "\x1b[1;1H";
+  static kClearScreenDown = "\x1b[0J";
+}
+
+function cursorTo(stream: File, x: number, y?: number) {
+  const uint8 = new TextEncoder().encode(CSI.kClear);
+  stream.write(uint8);
+}
+
+function clearScreenDown(stream: File) {
+  const uint8 = new TextEncoder().encode(CSI.kClearScreenDown);
+  stream.write(uint8);
+}
 
 // tslint:disable-next-line:no-any
 function getClassInstanceName(instance: any): string {
@@ -639,6 +655,12 @@ export class Console {
       this.log(); // When the collapsed state ended, outputs a sinle new line.
     }
   };
+
+  clear = (): void => {
+    this.indentLevel = 0;
+    cursorTo(stdout, 0, 0);
+    clearScreenDown(stdout);
+  };
 }
 
 /**

js/console_test.ts

@@ -1,5 +1,5 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-import { Console, libdeno, stringifyArgs, inspect } from "deno";
+import { Console, libdeno, stringifyArgs, inspect, write, stdout } from "deno";
 import { test, assertEqual } from "./test_util.ts";
 
 const console = new Console(libdeno.print);
@@ -116,7 +116,7 @@ test(function consoleTestStringifyCircular() {
   assertEqual(
     stringify(console),
     // tslint:disable-next-line:max-line-length
-    "Console { printFunc: [Function], log: [Function], debug: [Function], info: [Function], dir: [Function], warn: [Function], error: [Function], assert: [Function], count: [Function], countReset: [Function], time: [Function], timeLog: [Function], timeEnd: [Function], group: [Function], groupCollapsed: [Function], groupEnd: [Function], indentLevel: 0, collapsedAt: null }"
+    "Console { printFunc: [Function], log: [Function], debug: [Function], info: [Function], dir: [Function], warn: [Function], error: [Function], assert: [Function], count: [Function], countReset: [Function], time: [Function], timeLog: [Function], timeEnd: [Function], group: [Function], groupCollapsed: [Function], groupEnd: [Function], clear: [Function], indentLevel: 0, collapsedAt: null }"
   );
   // test inspect is working the same
   assertEqual(inspect(nestedObj), nestedObjExpected);
@@ -249,6 +249,24 @@ test(function consoleTestError() {
   }
 });
 
+test(function consoleTestClear() {
+  const stdoutWrite = stdout.write;
+  const uint8 = new TextEncoder().encode("\x1b[1;1H" + "\x1b[0J");
+  let buffer = new Uint8Array(0);
+
+  stdout.write = async u8 => {
+    const tmp = new Uint8Array(buffer.length + u8.length);
+    tmp.set(buffer, 0);
+    tmp.set(u8, buffer.length);
+    buffer = tmp;
+
+    return await write(stdout.rid, u8);
+  };
+  console.clear();
+  stdout.write = stdoutWrite;
+  assertEqual(buffer, uint8);
+});
+
 // Test bound this issue
 test(function consoleDetachedLog() {
   const log = console.log;
@@ -265,6 +283,7 @@ test(function consoleDetachedLog() {
   const consoleTimeEnd = console.timeEnd;
   const consoleGroup = console.group;
   const consoleGroupEnd = console.groupEnd;
+  const consoleClear = console.clear;
   log("Hello world");
   dir("Hello world");
   debug("Hello world");
@@ -279,4 +298,5 @@ test(function consoleDetachedLog() {
   consoleTimeEnd("Hello world");
   consoleGroup("Hello world");
   consoleGroupEnd();
+  console.clear();
 });