added a checkbox to set an offset to the first line

app/crashviewer.css

@@ -43,6 +43,7 @@ body {
 	font-family: 'Ubuntu', sans-serif;
 	font-size: 20px;
 	padding: 4px 8px;
+	height: 34px;
 }
 
 .toggleShow {
@@ -115,6 +116,28 @@ body {
 	padding: 4px 0px;
 }
 
+#firstLineSpan {
+	float: right;
+	font-size: 22px;
+	vertical-align: middle;
+}
+
+#enableFirstLine {
+	width: 21px;
+	height: 21px;
+	margin: 0px;
+	vertical-align: middle;
+	margin-right: 10px;
+}
+
+#firstLineValue {
+	font-family: 'Source Code Pro', monospace;
+	font-size: 16px;
+	width: 80px;
+	height: 30px;
+	margin-left: 10px;
+}
+
 .darkModeScrollbar::-webkit-scrollbar, .darkModeScrollbar::-webkit-scrollbar-track {
 	background-color: black;
 	width: 15px;

app/crashviewer.js

@@ -209,6 +209,13 @@ function printVersionWarning(vers) {
 
 function updateSource(srcMap) {
 	clearDecodedView();
+
+	var firstLine = 0;
+	var j = parseInt(appElements.firstLineValue.value);
+	if(!isNaN(j) && j > 1 && appElements.enableFirstLine.checked) {
+		firstLine = j - 1;
+	}
+
 	var sourceValue = appElements.inputTextArea.value;
 	var lines = sourceValue.split(/\r?\n/g);
 	var vers = extractVersionFromFile(lines);
@@ -239,7 +246,9 @@ function updateSource(srcMap) {
 						}
 					}
 					if(!isNaN(lineNo) && !isNaN(colNo)) {
-						var original = formatLine(srcMap.originalPositionFor({ line: lineNo, column: colNo }));
+						var newLineNumber = lineNo - firstLine;
+						if(newLineNumber > 0) {
+							var original = formatLine(srcMap.originalPositionFor({ line: newLineNumber, column: colNo }));
 							if(original !== null) {
 								if(firstToken.endsWith("line")) {
 									appElements.outputContent.appendChild(document.createTextNode(lines[i] + " "));
@@ -263,6 +272,7 @@ function updateSource(srcMap) {
 					}
 				}
 			}
+		}
 
 		appElements.outputContent.appendChild(document.createTextNode(lines[i] + "\n"));
 	}
@@ -420,6 +430,56 @@ function showFileChooser() {
 	fileChooserElement.click();
 }
 
+function changeFirstLineShading(en) {
+	if(en) {
+		appElements.firstLineText.style.color = "white";
+		appElements.firstLineValue.disabled = false;
+	}else {
+		appElements.firstLineText.style.color = "#999999";
+		appElements.firstLineValue.disabled = true;
+	}
+}
+
+var changeFirstLineTimout = -1;
+
+function handleChangeFirstLineEnabled() {
+	changeFirstLineTimout = -1;
+	var cookie = {};
+	cookie.enableFirstLine = appElements.enableFirstLine.checked;
+	var i = parseInt(appElements.firstLineValue.value);
+	var is_nan = isNaN(i);
+	if(!is_nan || cookie.enableFirstLine) {
+		if(is_nan || i < 1) {
+			i = 1;
+		}
+		cookie.firstLineValue = i;
+		window.localStorage.setItem("crashReportViewer_conf", JSON.stringify(cookie));
+	}
+	changeFirstLineShading(cookie.enableFirstLine);
+	if(!isShowingOriginal) {
+		updateDecodedPane();
+	}
+}
+
+function changeFirstLineEnabled() {
+	if(changeFirstLineTimout != -1) {
+		clearTimeout(changeFirstLineTimout);
+	}
+	changeFirstLineTimout = setTimeout(handleChangeFirstLineEnabled, 300);
+}
+
+function changeFirstLineEnabledImmediate() {
+	if(changeFirstLineTimout != -1) {
+		clearTimeout(changeFirstLineTimout);
+	}
+	var i = parseInt(appElements.firstLineValue.value);
+	var is_nan = isNaN(i);
+	if(is_nan || i < 1) {
+		appElements.firstLineValue.value = "1";
+	}
+	handleChangeFirstLineEnabled();
+}
+
 window.addEventListener("load", () => {
 
 	appElements = {
@@ -430,7 +490,10 @@ window.addEventListener("load", () => {
 		outputTextArea: document.getElementById("outputTextArea"),
 		outputContent: document.getElementById("outputContent"),
 		fetchingMessage: document.getElementById("fetchingMessage"),
-		loadingDots: document.getElementById("loadingDots")
+		loadingDots: document.getElementById("loadingDots"),
+		enableFirstLine: document.getElementById("enableFirstLine"),
+		firstLineText: document.getElementById("firstLineText"),
+		firstLineValue: document.getElementById("firstLineValue")
 	};
 
 	dotsInterval = setInterval(updateDots, 300);
@@ -452,6 +515,27 @@ window.addEventListener("load", () => {
 
 	appElements.sourceMaps.addEventListener("change", comboBoxChangeHandler);
 
+	appElements.enableFirstLine.addEventListener("change", changeFirstLineEnabledImmediate);
+	appElements.firstLineValue.addEventListener("propertychange", changeFirstLineEnabled);
+	appElements.firstLineValue.addEventListener("change", changeFirstLineEnabled);
+	appElements.firstLineValue.addEventListener("click", changeFirstLineEnabled);
+	appElements.firstLineValue.addEventListener("keyup", changeFirstLineEnabled);
+	appElements.firstLineValue.addEventListener("input", changeFirstLineEnabled);
+	appElements.firstLineValue.addEventListener("paste", changeFirstLineEnabled);
+
+	var cookie = window.localStorage.getItem("crashReportViewer_conf");
+	if(cookie) {
+		try {
+			cookie = JSON.parse(cookie);
+			if(cookie && typeof cookie.firstLineValue === "number") {
+				appElements.enableFirstLine.checked = !!cookie.enableFirstLine;
+				appElements.firstLineValue.value = "" + cookie.firstLineValue;
+				changeFirstLineShading(!!cookie.enableFirstLine);
+			}
+		}catch(e) {
+		}
+	}
+
 	fetch("sourceMaps.json")
 		.then((r) => r.json())
 		.then(sourceMapListLoaded)

app/index.html

@@ -28,6 +28,9 @@
 				<span id="fetchingMessage">Fetching source maps, please wait<span id="loadingDots"></span></span>
 				<span id="showOriginal" class="toggleShow toggleSelected" style="display:none;">Show Original</span>
 				<span id="showDecoded" class="toggleShow toggleShowDisabled" style="display:none;">Show Decoded</span>
+				<span id="firstLineSpan">
+					<input type="checkbox" id="enableFirstLine" />&nbsp;<span style="color:#999999;" id="firstLineText">First line:</span>&nbsp;<input type="text" pattern="[0-9]+" id="firstLineValue" disabled />
+				</span>
 			</p>
 		</div>
 		<div class="containerBody">