From dff1fa45bbcd41f8a2aa42d8b61255761b506ba8 Mon Sep 17 00:00:00 2001
From: Molly Lloyd <mollymerp@users.noreply.github.com>
Date: Thu, 5 Oct 2017 11:27:02 -0700
Subject: [PATCH] error if invalid 'before' argument is passed to Map#addLayer
 (#5401)

error if invalid 'before' argument is passed to Map#addLayer
---
 src/style/style.js            |  6 ++++++
 test/unit/style/style.test.js | 22 ++++++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/src/style/style.js b/src/style/style.js
index 31a26aab11b..c6ec6c1ddda 100644
--- a/src/style/style.js
+++ b/src/style/style.js
@@ -568,7 +568,13 @@ class Style extends Evented {
 
         layer.setEventedParent(this, {layer: {id: id}});
 
+
         const index = before ? this._order.indexOf(before) : this._order.length;
+        if (before && index === -1) {
+            this.fire('error', { message: new Error(`Layer with id "${before}" does not exist on this map.`)});
+            return;
+        }
+
         this._order.splice(index, 0, id);
 
         this._layers[id] = layer;
diff --git a/test/unit/style/style.test.js b/test/unit/style/style.test.js
index b67c91e00e4..2142dfaf365 100644
--- a/test/unit/style/style.test.js
+++ b/test/unit/style/style.test.js
@@ -1006,6 +1006,28 @@ test('Style#addLayer', (t) => {
         });
     });
 
+    t.test('fire error if before layer does not exist', (t) => {
+        const style = new Style(new StubMap());
+        style.loadJSON(createStyleJSON({
+            layers: [{
+                id: 'a',
+                type: 'background'
+            }, {
+                id: 'b',
+                type: 'background'
+            }]
+        }));
+        const layer = {id: 'c', type: 'background'};
+
+        style.on('style.load', () => {
+            style.on('error', (error)=>{
+                t.match(error.message, /does not exist on this map/);
+                t.end();
+            });
+            style.addLayer(layer, 'z');
+        });
+    });
+
     t.test('fires an error on non-existant source layer', (t) => {
         const style = new Style(new StubMap());
         style.loadJSON(util.extend(createStyleJSON(), {