+ core: add helper method to read text from file.

lib/core/src/helpers/index.ts

@@ -22,3 +22,4 @@ export * from './sticky';
 export * from './commands';
 export * from './run-js';
 export * from './select-file';
+export * from './read-file';

lib/core/src/helpers/read-file.ts

@@ -0,0 +1,12 @@
+export function readFile(file: File): Promise<string> {
+    return new Promise((resolve, reject) => {
+        const reader = new FileReader();
+        reader.onload = () => {
+            resolve(reader.result as string);
+        };
+        reader.onerror = (error) => {
+            reject(error);
+        };
+        reader.readAsText(file);
+    });
+}