With some research and some of your help I was able to create and comment some code I believe will help people understand Javascript Promises more clearly.
My question is, when I try to trigger a catch by intentionally misspelling the JSON file name, nothing happens. No error. No continue. Nothing. Why?
Why doesn't...
else reject( new Error( 'We could not load the URI: ' + uri ) );
...gets thrown?
URL for you to visualize without cross origin issues when getting JSON file.
Content of
resultset.json
[
{
"PK_USER_TIME_LOG_ID": 120,
"CLIENT_ID": 111,
"PROJECT_ID": 222,
"USER_ID": 465605,
"UTL_DTSTAMP": "2018-01-15 17:56:06",
"UTL_LATITUDE": "40.61105890",
"UTL_LONGITUDE": "-111.89993530",
"UTL_EVENT": "CLOCK IN",
"UTL_ACTION": "MEETING",
"UTL_DURATION": 3
},
{
"PK_USER_TIME_LOG_ID": 122,
"CLIENT_ID": 111,
"PROJECT_ID": 222,
"USER_ID": 465605,
"UTL_DTSTAMP": "2018-01-15 17:56:19",
"UTL_LATITUDE": "40.61105890",
"UTL_LONGITUDE": "-111.89993530",
"UTL_EVENT": "CLOCK IN",
"UTL_ACTION": "TRAVEL",
"UTL_DURATION": 5
},
{
"PK_USER_TIME_LOG_ID": 123,
"CLIENT_ID": 111,
"PROJECT_ID": 222,
"USER_ID": 465605,
"UTL_DTSTAMP": "2018-01-15 17:56:24",
"UTL_LATITUDE": "40.61105890",
"UTL_LONGITUDE": "-111.89993530",
"UTL_EVENT": "CLOCK IN",
"UTL_ACTION": "TEAR OUT",
"UTL_DURATION": 3
}
]
Javascript Promise Code Updated 1/18/2018
$(document).ready(function() {
console.log('1. Document is ready.');
// Run the App.
runApplication();
});
// anything we would like to run *** BEFORE *** getURI( obj ) function is called.
var runFirst = function runFirst() {
console.log( '2. Promise > runFirst() function called.' );
};
// We create a variable called getURI and assign it a function getURI( uri )
var getURI = function getURI( uri ) {
console.log('3. Promise > getURI( uri ) function called.');
// We then create a new Promise (Which is a wrapper..) to return.
return new Promise( function( resolve, reject ) {
// Our JSON request..
$.getJSON( uri, function( data ) {
// if data is not defined OR an empty string...
if (data =! true || data.length < 1) {
// Create a new error and...
var error = new Error();
// Inject an error status code of 204.
error.status = 204;
// Reject Promise with custom error.
reject( error );
} else {
// Continue...
resolve( data );
}
}).fail( reject );
// Invoke Promise Reject so we can handle the Ajax .fail() by status code.
}); // End promise.
};
// obj edit In Progress.
var processData = function processData( obj ) {
console.log( '3.2 Promise > processData( obj ) function called.' );
// Parse array of arrays if we have to. (For resultSet containing more than one record..)
$.each(obj, function( i, row ) {
// DO...
// Get current row.USER_ID from current row.
console.log('3.2.1 Get: row.USER_ID = '+ row.USER_ID);
// AND OR..
// Set current row.USER_ID to something else..
row.USER_ID = 'something else..';
// AND OR..
// Push a new_element into current row..
row.new_element = 'something new!';
//THEN...
// Get updated row.USER_ID from current row.
console.log('3.2.2 Set: '+ row.USER_ID);
}); // End jQuery for each loop
// Return Original and/or Augmented fectched object.
return Promise.resolve(obj);
};
// obj Done editing. Now we render it. (Display the most up to date version of it.)
var renderData = function renderData( obj ) {
console.log( '3.3 Promise > renderData( obj ) function called.' );
//console.log( obj );
// Return fectched object after being proccessed by processData.
return Promise.resolve(obj);
};
// anything we would like to run *** AFTER *** our getURI( uri ) function is called.
var runLast = function runLast( obj ) {
console.log( '3.4 Promise > runLast() function called.' );
console.log( '3.5 Promise > Successful $.getJSON() response received.' );
// Return fectched object after being proccessed by renderData.
return Promise.resolve(obj);
};
// error handling for $.getJSON() and anything else.
var handleError = function handleError( error ) {
console.log( 'Error - Promise > handleError( error ) function called.' );
console.log( 'Error - We found an error while fetching and/or augmenting some data.' );
// Error if $.getJSON() is status: 204 No Content.
if (error.status == 204) {
console.error( '$.getJSON() .status: ' + error.status + ' - No Content.');
return;
}
// Error if $.getJSON() is status: 404 Not Found.
if (error.status == 404) {
console.error( '$.getJSON() .status: ' + error.status + ' - Not Found.');
return;
}
// Error unknown...
console.log(error);
};
// We create a variable called runApplication and assign it a function runApplication()
var runApplication = function runApplication() {
console.log( '1.1 runApplication() function called.' );
// Similar to Ajax beforeSend()..
runFirst();
// getURI request execution order...
getURI( 'resultset.json' ) // entering Promise...
.then( processData ) // process the data...
.then( renderData ) // render the processed data...
.then( runLast ) // finalize...
.catch( handleError ); // catch our Ajax and Custom errors.)
};
Answer
If you want catch ajax error, add method .fail after. As doc says, $.getJSON has silent errors..
$(document).ready(function() {
console.log('1. Document is ready.');
});
// We create a variable called getURI and assign it a function getURI( uri )
var getURI = function getURI( uri ) {
// We then create a new Promise (Which is wrapper..) to return.
return new Promise( function( resolve, reject ) {
// Asynch request for JSON data... (Because that's what we are getting from the server.)
// ajax commented due to snippet
$.getJSON( uri, function( data ) {
// if we got something, resolve promise
if ( data ) resolve( data );
// else reject promise and throw an Error.
else reject( new Error( 'We could not load the URI: ' + uri ) );
}).fail(reject)
// End get.
}); // End promise.
};
// anything we would like to run *** BEFORE *** getURI( obj ) function is called.
var runFirst = function runFirst() {
console.log( '3.1 Promise > runFirst() function called.' );
};
// obj being edited. Status in progress.
var processData = function processData( obj ) {
console.log( '3.2 Promise > processData( obj ) function called.' );
// Parse array of arrays if we have to. (For resultSet containing more than one record..)
$.each(obj, function( row_idx, row ) {
// DO...
// Get current row.USER_ID from current row.
console.log('3.2.1 Get: '+ row.USER_ID);
// AND OR..
// Set current row.USER_ID to something else..
row.USER_ID = 'something else..';
// AND OR..
// Push new row.new_element to something new!
row.new_element = 'something new!';
//THEN..
// Get updated row.USER_ID from current row.
console.log('3.2.2 Set: '+ row.USER_ID);
}); // END jQuery for each loop
// Return Formated Object.
return Promise.resolve(obj);
};
// obj Done editing. Now we render it. (Display the most up to date version of it.)
var renderData = function renderData( obj ) {
console.log( '3.3 Promise > renderData( obj ) function called.' );
//console.log( obj );
return Promise.resolve(obj);
};
// anything we would like to run *** AFTER *** our getURI( uri ) function is called.
var runLast = function runLast(obj) {
console.log( '3.4 Promise > runLast() function called.' );
return Promise.resolve(obj);
};
// finally handleError( error ); how we handle our catch function.
var handleError = function handleError( error ) {
console.log( '3.x Promise > handleError( error ) function called.' );
console.log( '3.x We found an error while fetching and augmenting some data.' );
console.error( error );
};
// We create a variable called runApplication and assign it a function runApplication()
var runApplication = function runApplication() {
// Similar to Ajax beforeSend()..
runFirst();
// getURI request execution order...
getURI( 'resultset.json' )
.then( processData )
.then( renderData )
.then( runLast )
.catch( handleError );
};
// I think you can guess what this does.
runApplication();
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