Add support for debug in browser from window object (#704)

Allows to set the window.debugKuzzleSdk variable to true to activate debug mode from the browser.
Other changes

    avoid multiple calls to process.env
    print directly the object in the browser

Author: Adrien Maret

doc/7/essentials/debugging/index.md

@@ -36,8 +36,6 @@ export DEBUG=kuzzle-sdk
 # Run your program
 ```
 
-In the Browser, you need to add the `debugKuzzleSdk` search param in the URL.
-
-```
-http://my-application.by/devices?debugKuzzleSdk
-```
+In the Browser, you can:
+ - add the `debugKuzzleSdk` search param in the URL. (e.g. `http://my-application.by/<path>?debugKuzzleSdk`)
+ - set the `window.debugKuzzleSdk` variable to `true`

src/utils/debug.js

@@ -1,20 +1,24 @@
+let NODE_DEBUG;
+
 function shouldDebug () {
   if (typeof window === 'undefined') {
-    const debugString = process.env.DEBUG || '';
+    // Avoid multiple calls to process.env
+    if (! NODE_DEBUG) {
+      NODE_DEBUG = (process.env.DEBUG || '').includes('kuzzle-sdk');
+    }
 
-    return debugString.includes('kuzzle-sdk');
+    return NODE_DEBUG;
   }
 
-  const url = new URL(window.location);
-
-  return url.searchParams.get('debugKuzzleSdk') !== null;
+  return window.debugKuzzleSdk || new URL(window.location).searchParams.get('debugKuzzleSdk') !== null;
 }
 
 /**
  * Print debug only if activated
  *
- * In Node.js, you can set the `DEBUG=kuzzle-sdk` env variable
+ * In Node.js, you can set the `DEBUG=kuzzle-sdk` env variable.
  * In a browser, you can add the `?debugKuzzleSdk` in the URL
+ * or set `window.debugKuzzleSdk` = true
  */
 function debug (message, obj) {
   if (! shouldDebug()) {
@@ -25,8 +29,11 @@ function debug (message, obj) {
   console.log(message);
 
   if (obj) {
+    // Browser console can print directly objects
+    const toPrint = typeof window === 'undefined' ? JSON.stringify(obj) : obj;
+
     // eslint-disable-next-line no-console
-    console.log(JSON.stringify(obj));
+    console.log(toPrint);
   }
 }