Update index.js

Add "deleteSheet" function

lib/index.js

@@ -30,6 +30,36 @@ module.exports = (function() {
         }
     };
 
+  /**
+    * Delete unused sheets if needed
+    */
+	Workbook.prototype.deleteSheet = function(sheetName){
+		var self = this;
+	    var sheet = self.loadSheet(sheetName);
+		  
+		Object.keys(self.archive.files).forEach(key=>{
+			if (key.indexOf(sheet.id) != -1)
+				delete self.archive.files[key];
+		})
+		  
+		var i = self.sheets.findIndex(el=> el.id == sheet.id);
+		self.sheets.splice(i, 1);	
+		  
+		var el = self.workbook._children.find(item=>item.tag==='sheets');
+		if (!el) throw new Error("Template file contain errors");
+		//	sheet.rId = el._children[i].attrib['r:id'];
+		el._children.splice(i,1);
+		  
+		el = self.workbook._children.find(item=>item.tag==='definedNames');
+		if (el) {
+			el._children.splice(i,1);
+			el._children.forEach((item, index)=>{item.attrib.localSheetId = String(index)})	// fix to avoid opening errors
+		}
+		  
+		self.archive.file(sheet.filename, etree.tostring(sheet.root));
+		 self.archive.file(self.workbookPath, etree.tostring(self.workbook));
+	};
+
     /**
      * Load a .xlsx file from a byte array.
      */