sp15_taxAllTerms.js

$(document).ready(function(){   
  
	var scriptbase = _spPageContextInfo.webServerRelativeUrl + "_layouts/15/";
	
	$.getScript(scriptbase + "SP.Runtime.js",
        function () {
            $.getScript(scriptbase + "SP.js", function(){
            
            	$.getScript(scriptbase + "SP.Taxonomy.js", execOperation);

            });
        }
    );

});

function execOperation(){
	
    //Current Context
    var context = SP.ClientContext.get_current();
	
    //Current Taxonomy Session
    var taxSession = SP.Taxonomy.TaxonomySession.getTaxonomySession(context);
    
    //Term Stores
    var termStores = taxSession.get_termStores();
    
    //Name of the Term Store from which to get the Terms.
    var termStore = termStores.getByName("Taxonomy_Dmxzz8tIBzk8wNVKQpJ+xA==");
    
    //GUID of Term Set from which to get the Terms.
    var termSet = termStore.getTermSet("b49f64b3-4722-4336-9a5c-56c326b344d4");
    
    var terms = termSet.getAllTerms();
    
    context.load(terms);
		
    context.executeQueryAsync(function(){
	
  	var termEnumerator = terms.getEnumerator();
  		
  	var termList = "Terms: \n";
  		
		while(termEnumerator.moveNext()){
			
			var currentTerm = termEnumerator.get_current();
			
			termList += currentTerm.get_name() + "\n";
	
		} 
		
		  alert(termList);
   		
    },function(sender,args){
	
	      console.log(args.get_message());
	
    });
 
}