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Here are a collection of useful JavaScript utility methods. I frequently use these utility methods in my project work and I hope you find them useful as well. 

You can suggest any useful JavaScript utility methods in the comment section so that I can add them to this list. For explanation, please refer to comments on each method that would be self-descriptive.

JavaScript Utility Methods

     /**
      * Parse JSON string or throw error
      */
     function parseJSON(data) {
         data = data || "";
         try {
             return JSON.parse(data);
         } catch (error) {
             throw new Error({
                 type: 'JSON.parse',
                 message: error.stack,
                 reason: error.message
             });
         }
     }
     /**
      * Safely parse JSON strings (no errors)
      */
     function toJSON(data) {
         data = data || "";
         try {
             return JSON.parse(data);
         } catch (error) {
             return {
                 type: 'JSON.parse',
                 message: error.stack,
                 reason: error.message
             };
         }
     }

     /**
      * Check empty object
      */
     function checkEmptyObject(obj) {
         for (var key in obj) {
             if (obj.hasOwnProperty(key))
                 return false;
         }
         return true;
     }

     /**
      * Check if the string is empty or null
      */
     function checkNotNullAndNotEmpty(data) {
         if (data !== null && data !== '') {
             return true;
         }
         return false;
     }

     /**
      * Check if the variable is undefined
      */
     function isUndefined(data) {
         if (data === "undefined") {
             return true;
         }
         return false;
     }

     /**
      * "Safer" String.toLowerCase()
      */
     function lowerCase(str) {
         return str.toLowerCase();
     }

     /**
      * "Safer" String.toUpperCase()
      */
     function upperCase(str) {
         return str.toUpperCase();
     }

     /**
      * UPPERCASE first char of each word.
      */
     function properCase(str) {
         return lowerCase(str).replace(/^\w|\s\w/g, upperCase);
     }

     /**
      * UPPERCASE first char of each sentence and lowercase other chars.
      */
     function sentenceCase(str) {
         // Replace first char of each sentence (new line or after '.\s+') to
         // UPPERCASE
         return lowerCase(str).replace(/(^\w)|\.\s+(\w)/gm, upperCase);
     }


     /**
      * Searches for a given substring
      */
     function contains(str, substring, fromIndex) {
         return str.indexOf(substring, fromIndex) !== -1;
     }

     /**
      * Escapes a string for insertion into HTML.
      */
     function escapeHtml(str) {
         str = str
             .replace(/&/g, '&')
             .replace(/</g, '&lt;')
             .replace(/>/g, '&gt;')
             .replace(/'/g, '&#39;')
             .replace(/"/g, '&quot;');

         return str;
     }

     /**
      * Unescapes HTML special chars
      */
     function unescapeHtml(str) {
         str = str
             .replace(/&amp;/g, '&')
             .replace(/&lt;/g, '<')
             .replace(/&gt;/g, '>')
             .replace(/&#39;/g, "'")
             .replace(/&quot;/g, '"');
         return str;
     }

     /**
      * Remove HTML tags from string.
      */
     function stripHtmlTags(str) {
         return str.replace(/<[^>]*>/g, '');
     }