diff --git a/src/common/util.ts b/src/common/util.ts
index d8ef62f2..2d40cbc6 100644
--- a/src/common/util.ts
+++ b/src/common/util.ts
@@ -461,7 +461,7 @@ export function getWithBinary(url:string, success:(text:string|Uint8Array)=>void
     } else if (oReq.status == 404) {
       success(null);
     } else {
-      throw "Error " + oReq.status + " loading " + url;
+      throw Error("Error " + oReq.status + " loading " + url);
     }
   }
   oReq.send(null);
diff --git a/src/ide/pixeleditor.ts b/src/ide/pixeleditor.ts
index 8409712f..b4552bfa 100644
--- a/src/ide/pixeleditor.ts
+++ b/src/ide/pixeleditor.ts
@@ -442,7 +442,7 @@ export class TextDataNode extends CodeProjectDataNode {
   }
   updateLeft() {
     if (this.right.words.length != this.words.length)
-      throw "Expected " + this.right.words.length + " bytes; image has " + this.words.length;
+      throw Error("Expected " + this.right.words.length + " bytes; image has " + this.words.length);
     this.words = this.right.words;
     // TODO: reload editors?
     var datastr = this.text.substring(this.start, this.end);
@@ -715,9 +715,9 @@ export class NESNametableConverter extends Compositor {
     for (var row=0; row<this.rows; row++) {
       for (var col=0; col<this.cols; col++) {
          var name = this.words[this.baseofs + a];
-         if (typeof name === 'undefined') throw "No name for address " + this.baseofs + " + " + a;
+         if (typeof name === 'undefined') throw Error("No name for address " + this.baseofs + " + " + a);
          var t = this.tilemap[name];
-         if (!t) throw "No tilemap found for tile index " + name;
+         if (!t) throw Error("No tilemap found for tile index " + name);
          attraddr = (a & 0x2c00) | 0x3c0 | (a & 0x0C00) | ((a >> 4) & 0x38) | ((a >> 2) & 0x07);
          var attr = this.words[attraddr];
          var tag = name ^ (attr<<9) ^ 0x80000000;
diff --git a/src/ide/project.ts b/src/ide/project.ts
index 682d9465..2c33aba3 100644
--- a/src/ide/project.ts
+++ b/src/ide/project.ts
@@ -245,7 +245,7 @@ export class CodeProject {
   }
 
   sendBuild() {
-    if (!this.mainpath) throw "need to call setMainFile first";
+    if (!this.mainpath) throw Error("need to call setMainFile first");
     var maindata = this.getFile(this.mainpath);
     // if binary blob, just return it as ROM
     if (maindata instanceof Uint8Array) {
diff --git a/src/ide/services.ts b/src/ide/services.ts
index 763ef6d8..d8e06cb7 100644
--- a/src/ide/services.ts
+++ b/src/ide/services.ts
@@ -156,7 +156,7 @@ export class GithubService {
             return sess.repo.git.trees(subtree.sha).fetch();
           }
         }
-        throw "Cannot find subtree '" + sess.subtreepath + "' in tree " + tree.sha;
+        throw Error("Cannot find subtree '" + sess.subtreepath + "' in tree " + tree.sha);
       }
       return tree;
     })
@@ -207,7 +207,7 @@ export class GithubService {
       if (m) {
         console.log("platform id: '" + m[1] + "'");
         if (sess.platform_id && !sess.platform_id.startsWith(m[1]))
-          throw "Platform mismatch: Repository is " + m[1] + ", you have " + this.project.platform_id + " selected.";
+          throw Error("Platform mismatch: Repository is " + m[1] + ", you have " + this.project.platform_id + " selected.");
         sess.platform_id = m[1];
       }
       // bind to repository
@@ -295,7 +295,7 @@ export class GithubService {
     return this.getGithubHEADTree(ghurl).then( (session) => {
       sess = session;
       if (sess.subtreepath) {
-        throw "Sorry, right now you can only commit files to the root directory of a repository.";
+        throw Error("Sorry, right now you can only commit files to the root directory of a repository.");
       }
       return Promise.all(files.map( (file) => {
         if (typeof file.data === 'string') {
diff --git a/src/machine/sms.ts b/src/machine/sms.ts
index f79faf26..4b21297c 100644
--- a/src/machine/sms.ts
+++ b/src/machine/sms.ts
@@ -191,7 +191,7 @@ export class SMS extends SG1000 {
           this.romPageMask = (data.length >> 14) - 1; // div $4000
           break;
         default:
-          throw "Unknown rom size: $" + hex(data.length);
+          throw Error("Unknown rom size: $" + hex(data.length));
       }
     }
     //console.log("romPageMask: " + hex(this.romPageMask));
diff --git a/src/platform/vector.ts b/src/platform/vector.ts
index a5a572e9..a0abd6a5 100644
--- a/src/platform/vector.ts
+++ b/src/platform/vector.ts
@@ -122,7 +122,7 @@ var AtariVectorPlatform = function(mainElement) {
 
   this.loadROM = function(title, data) {
     if(data.length != 0x2000) {
-      throw "ROM length must be == 0x2000";
+      throw Error("ROM length must be == 0x2000");
     }
     rom = data.slice(0,0x1800);
     vecrom = data.slice(0x1800,0x2000);
diff --git a/src/platform/verilog.ts b/src/platform/verilog.ts
index e30e7ef9..ca0eeb55 100644
--- a/src/platform/verilog.ts
+++ b/src/platform/verilog.ts
@@ -140,12 +140,12 @@ export function VL_READMEM_W(ishex,width,depth,array_lsb,fnwords,filename,memp,s
   var strfn = byteArrayToString(barr); // convert to string
   // parse hex/binary file
   var strdata = current_project.getFile(strfn) as string;
-  if (strdata == null) throw "Could not $readmem '" + strfn + "'";
+  if (strdata == null) throw Error("Could not $readmem '" + strfn + "'");
   var data = strdata.split('\n').filter(s => s !== '').map(s => parseInt(s, ishex ? 16 : 2));
   console.log('$readmem', ishex, strfn, data.length);
   // copy into destination array
-  if (memp === null) throw "No destination array to $readmem " + strfn;
-  if (memp.length < data.length) throw "Destination array too small to $readmem " + strfn;
+  if (memp === null) throw Error("No destination array to $readmem " + strfn);
+  if (memp.length < data.length) throw Error("Destination array too small to $readmem " + strfn);
   for (i=0; i<data.length; i++)
     memp[i] = data[i];
 }
diff --git a/src/worker/workermain.ts b/src/worker/workermain.ts
index c3d133fc..966786ce 100644
--- a/src/worker/workermain.ts
+++ b/src/worker/workermain.ts
@@ -353,7 +353,7 @@ function gatherFiles(step:BuildStep, options?:BuildOptions) {
   }
   else if (step.code) {
     var path = step.path ? step.path : options.mainFilePath; // TODO: what if options null
-    if (!path) throw "need path or mainFilePath";
+    if (!path) throw Error("need path or mainFilePath");
     var code = step.code;
     var entry = putWorkFile(path, code);
     step.path = path;
@@ -378,7 +378,7 @@ function gatherFiles(step:BuildStep, options?:BuildOptions) {
 
 function populateFiles(step:BuildStep, fs, options?:BuildOptions) {
   gatherFiles(step, options);
-  if (!step.files) throw "call gatherFiles() first";
+  if (!step.files) throw Error("call gatherFiles() first");
   for (var i=0; i<step.files.length; i++) {
     var path = step.files[i];
     populateEntry(fs, path, workfs[path], options);
@@ -413,7 +413,7 @@ function populateExtraFiles(step:BuildStep, fs, extrafiles) {
 }
 
 function staleFiles(step:BuildStep, targets:string[]) {
-  if (!step.maxts) throw "call populateFiles() first";
+  if (!step.maxts) throw Error("call populateFiles() first");
   // see if any target files are more recent than inputs
   for (var i=0; i<targets.length; i++) {
     var entry = workfs[targets[i]];
@@ -425,7 +425,7 @@ function staleFiles(step:BuildStep, targets:string[]) {
 }
 
 function anyTargetChanged(step:BuildStep, targets:string[]) {
-  if (!step.maxts) throw "call populateFiles() first";
+  if (!step.maxts) throw Error("call populateFiles() first");
   // see if any target files are more recent than inputs
   for (var i=0; i<targets.length; i++) {
     var entry = workfs[targets[i]];
@@ -509,7 +509,7 @@ function setupFS(FS, name:string) {
   var WORKERFS = FS.filesystems['WORKERFS'];
   if (name === '65-vector') name = '65-sim6502'; // TODO
   if (name === '65-atari7800') name = '65-sim6502'; // TODO
-  if (!fsMeta[name]) throw "No filesystem for '" + name + "'";
+  if (!fsMeta[name]) throw Error("No filesystem for '" + name + "'");
   FS.mkdir('/share');
   FS.mount(WORKERFS, {
     packages: [{ metadata: fsMeta[name], blob: fsBlob[name] }]
@@ -1491,7 +1491,7 @@ function compileJSASM(asmcode:string, platform, options, is_inline) {
   var includes = [];
   asm.loadJSON = (filename:string) => {
     var jsontext = getWorkFileAsString(filename);
-    if (!jsontext) throw "could not load " + filename;
+    if (!jsontext) throw Error("could not load " + filename);
     return JSON.parse(jsontext);
   };
   asm.loadInclude = function(filename) {
@@ -2106,7 +2106,7 @@ function executeBuildSteps() {
     var step = buildsteps.shift(); // get top of array
     var platform = step.platform;
     var toolfn = TOOLS[step.tool];
-    if (!toolfn) throw "no tool named " + step.tool;
+    if (!toolfn) throw Error("no tool named " + step.tool);
     step.params = PLATFORM_PARAMS[getBasePlatform(platform)];
     try {
       step.result = toolfn(step);
diff --git a/test/cli/testgithub.js b/test/cli/testgithub.js
index 74ae8945..08d6bea1 100644
--- a/test/cli/testgithub.js
+++ b/test/cli/testgithub.js
@@ -64,7 +64,7 @@ describe('Store', function() {
     var store = mstore.createNewPersistentStore('_FOO', function(store) {
       var gh = newGH(store, '_FOO');
       gh.importAndPull('https://github.com/pzpinfo/testrepo1557326056720').catch( (e) => {
-        assert.ok(e.startsWith('Platform mismatch'));
+        assert.ok(e.message.startsWith('Platform mismatch'));
         done();
       });
     });
@@ -145,7 +145,7 @@ describe('Store', function() {
       gh.commit('https://github.com/brovador/NESnake/tree/master/src', 'test commit', files)
       .catch( (e) => {
         console.log(e);
-        assert.equal(e, 'Sorry, right now you can only commit files to the root directory of a repository.');
+        assert.equal(e.message, 'Sorry, right now you can only commit files to the root directory of a repository.');
         done();
       });
       /*.then( (sess) => {