allow formatter to return string

Author: mbostock

src/marks/tip.js

@@ -146,11 +146,18 @@ export class Tip extends Mark {
               this.setAttribute("stroke", "none");
               // iteratively render each channel value
               const names = new Set();
-              for (const line of format.call(mark, i, sources, scales, values)) {
-                const {name = ""} = line;
-                if (name && names.has(name)) continue;
-                else names.add(name);
-                renderLine(that, line);
+              const lines = format.call(mark, i, sources, scales, values);
+              if (typeof lines === "string") {
+                for (const line of mark.splitLines(lines)) {
+                  renderLine(that, {value: mark.clipLine(line)});
+                }
+              } else {
+                for (const line of lines) {
+                  const {name = ""} = line;
+                  if (name && names.has(name)) continue;
+                  else names.add(name);
+                  renderLine(that, line);
+                }
               }
             })
           )
@@ -305,11 +312,8 @@ function getSources({channels}) {
   return sources;
 }
 
-function* formatTitle(i, {title}) {
-  const text = title.value[i];
-  for (const line of this.splitLines(formatDefault(text))) {
-    yield {name: "", value: this.clipLine(line)};
-  }
+function formatTitle(i, {title}) {
+  return formatDefault(title.value[i]);
 }
 
 function* formatChannels(i, channels, scales, values) {