因為業務需要， 需要在使用Webview的時候，動態的載入js檔案到頁面中，之前SDK Target版本為16 ， 無論JS檔案多大，使用一切正常~

近期將target版本改為了19 ，發現存在js過大的時候，使用4.4以上版本執行專案，JS檔案不執行。

檢視原始碼發現在4.4版本以上核心對處理js做了區別處理：

495    @Override
496    public void loadUrl(final String url, Map<String, String> additionalHttpHeaders) {
497        // TODO: We may actually want to do some sanity checks here (like filter about://chrome).
498
499        // For backwards compatibility, apps targeting less than K will have JS URLs evaluated
500        // directly and any result of the evaluation will not replace the current page content.
501        // Matching Chrome behavior more closely; apps targetting >= K that load a JS URL will
502        // have the result of that URL replace the content of the current page.
503        final String JAVASCRIPT_SCHEME = "javascript:";
504        if (mAppTargetSdkVersion < Build.VERSION_CODES.KITKAT &&
505                url != null && url.startsWith(JAVASCRIPT_SCHEME)) {
506            mFactory.startYourEngines(true);
507            if (checkNeedsPost()) {
508                mRunQueue.addTask(new Runnable() {
509                    @Override
510                    public void run() {
511                        mAwContents.evaluateJavaScriptEvenIfNotYetNavigated(
512                                url.substring(JAVASCRIPT_SCHEME.length()));
513                    }
514                });
515            } else {
516                mAwContents.evaluateJavaScriptEvenIfNotYetNavigated(
517                        url.substring(JAVASCRIPT_SCHEME.length()));
518            }
519            return;
520        }
521
522        LoadUrlParams params = new LoadUrlParams(url);
523        if (additionalHttpHeaders != null) params.setExtraHeaders(additionalHttpHeaders);
524        loadUrlOnUiThread(params);
525    }
 

632    public void evaluateJavaScript(String script, ValueCallback<String> resultCallback) {
633        checkThread();
634        mAwContents.evaluateJavaScript(script, resultCallback);
635    }

Asynchronously evaluates JavaScript in the context of the currently displayed page. If non-null, |resultCallback| will be invoked with any result returned from that execution. This method must be called on the UI thread and the callback will be made on the UI thread.

Parameters
script	the JavaScript to execute.
resultCallback	A callback to be invoked when the script execution completes with the result of the execution (if any). May be null if no notificaion of the result is required.
 

另外其實還有個偷懶的解決方法：因為loadurl區分版本是用的target ， 那麼把target改小點唄，但是版本早晚要升上來， 治標不治本。