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I'm trying to create an array of objects by reading in a json. This is the relevant code:

//president object consctructor
function president(a_presName, a_presDates, a_presNick, a_presImage) {
    this.presName=a_presName;
    this.presDates=a_presDates;
    this.presNick=a_presNick;
    this.presImage=a_presImage;
}


var myPres = new Array();

$(document).ready(function() {



    $.getJSON('Presidents.json', function(data) {


        $.each(data.presidents, function (i, item) {
            myPres[i]=new president(item.presName, item.presDates, item.presNick, item.PresImage);
        });

    });  //end getJSON
    document.write(myPres[1].presName);
}); //end doc ready

And this is the json:

{ "presidents": [ { "presName":"George Washington", "presDates":"1789-1797", "presNick":"Father of His Country", "presImage":"gwashington.gif" }, { "presName":"John Adams", "presDates":"1797-1801", "presNick":"Atlas of Independence", "presImage":"jadams.gif" }, { "presName":"Thomas Jefferson", "presDates":"1801-1809", "presNick":"Sage of Monticello", "presImage":"tjefferson.gif" }, { "presName":"James Madison", "presDates":"1809-1817", "presNick":"Father of the Constitution", "presImage":"jmadison.gif" }, { "presName":"James Monroe", "presDates":"1817-1825", "presNick":"Era-of-Good-Feeling President", "presImage":"jmonroe.gif" }, { "presName":"John Quincy Adams", "presDates":"1825-1829", "presNick":"Old Man Eloquent", "presImage":"jqadams.gif" }, { "presName":"Andrew Jackson", "presDates":"1829-1837", "presNick":"Old Hickory", "presImage":"ajackson.gif" }, { "presName":"Martin Van Buren", "presDates":"1837-1841", "presNick":"The Little Magician", "presImage":"mvanburen.gif" }, { "presName":"William Henry Harrison", "presDates":"1841", "presNick":"Old Tippecanoe", "presImage":"whharrison.gif" }, { "presName":"John Tyler", "presDates":"1841-1845", "presNick":"Accidental President", "presImage":"jtyler.gif" }, { "presName":"James Knox Polk", "presDates":"1845-1849", "presNick":"Young Hickory", "presImage":"jkpolk.gif" }, { "presName":"Zachary Taylor", "presDates":"1849-1850", "presNick":"Old Rough and Ready", "presImage":"ztaylor.gif" }, { "presName":"Millard Fillmore", "presDates":"1850-1853", "presNick":"The American Louis Philippe", "presImage":"mfillmore.gif" }, { "presName":"Franklin Pierce", "presDates":"1853-1857", "presNick":"Young Hickory of the Granite Hills", "presImage":"fpierce.gif" }, { "presName":"James Buchanan", "presDates":"1857-1861", "presNick":"Old Buck", "presImage":"jbuchanan.gif" }, { "presName":"Abraham Lincoln", "presDates":"1861-1865", "presNick":"Honest Abe", "presImage":"alincoln.gif" }, { "presName":"Andrew Johnson", "presDates":"1865-1869", "presNick":"None", "presImage":"ajohnson.gif" }, { "presName":"Ulysses Simpson Grant", "presDates":"1869-1877", "presNick":"Hero of Appomattox", "presImage":"usgrant.gif" }, { "presName":"Rutherford Birchard Hayes", "presDates":"1877-1881", "presNick":"Dark-Horse President", "presImage":"rbhayes.gif" }, { "presName":"James Abram Garfield", "presDates":"1881", "presNick":"None", "presImage":"jagarfield.gif" }, { "presName":"Chester Alan Arthur", "presDates":"1881-1885", "presNick":"The Gentleman Boss", "presImage":"caarthur.gif" }, { "presName":"Grover Cleveland", "presDates":"1885-1889", "presNick":"None", "presImage":"gcleveland.gif" }, { "presName":"Benjamin Harrison", "presDates":"1889-1893", "presNick":"Kid Gloves Harrison", "presImage":"bharrison.gif" }, { "presName":"Grover Cleveland", "presDates":"1893-1897", "presNick":"None", "presImage":"gcleveland.gif" }, { "presName":"William McKinley", "presDates":"1897-1901", "presNick":"Idol of Ohio", "presImage":"wmckinley.gif" }, { "presName":"Theodore Roosevelt", "presDates":"1901-1909", "presNick":"Trust-Buster", "presImage":"troosevelt.gif" }, { "presName":"William Howard Taft", "presDates":"1909-1913", "presNick":"None", "presImage":"whtaft.gif" }, { "presName":"Woodrow Wilson", "presDates":"1913-1921", "presNick":"Schoolmaster in Politics", "presImage":"wwilson.gif" }, { "presName":"Warren Gamaliel Harding", "presDates":"1921-1923", "presNick":"None", "presImage":"wgharding.gif" }, { "presName":"Calvin Coolidge", "presDates":"1923-1929", "presNick":"Silent Cal", "presImage":"ccoolidge.gif" }, { "presName":"Herbert Clark Hoover", "presDates":"1929-1933", "presNick":"None", "presImage":"hchoover.gif" }, { "presName":"Franklin Delano Roosevelt", "presDates":"1933-1945", "presNick":"FDR", "presImage":"fdroosevelt.gif" }, { "presName":"Harry S. Truman", "presDates":"1945-1953", "presNick":"Give 'Em Hell Harry", "presImage":"hstruman.gif" }, { "presName":"Dwight David Eisenhower", "presDates":"1953-1961", "presNick":"Ike", "presImage":"ddeisenhower.gif" }, { "presName":"John Fitzgerald Kennedy", "presDates":"1961-1963", "presNick":"JFK", "presImage":"jfkennedy.gif" }, { "presName":"Lyndon Baines Johnson", "presDates":"1963-1969", "presNick":"LBJ", "presImage":"lbjohnson.gif" }, { "presName":"Richard Milhous Nixon", "presDates":"1969-1974", "presNick":"None", "presImage":"rmnixon.gif" }, { "presName":"Gerald Rudolph Ford", "presDates":"1974-1977", "presNick":"Jerry", "presImage":"grford.gif" }, { "presName":"James Earl Carter Jr.", "presDates":"1977-1981", "presNick":"Jimmy", "presImage":"jecarter.gif" }, { "presName":"Ronald Wilson Reagan", "presDates":"1981-1989", "presNick":"The Gipper", "presImage":"rwreagan.gif" }, { "presName":"George Herbert Walker Bush", "presDates":"1989-1993", "presNick":"Poppy", "presImage":"ghwbush.gif" }, { "presName":"William Jefferson Clinton", "presDates":"1993-2001", "presNick":"Bill", "presImage":"wjclinton.gif" }, { "presName":"George Walker Bush", "presDates":"2001-2009", "presNick":"W", "presImage":"gwbush.gif" }, { "presName":"Barack Hussein Obama", "presDates":"2009-", "presNick":"None", "presImage":"bhobama.gif" } ] }

When I use the document.write to test it works fine if it's placed right before }); //end getJSON, but if it's place immediately after it is null. What am I missing?

share|improve this question
4  
You're missing the fact that AJAX calls are asynchronous by default. –  DCoder May 6 '12 at 16:25
1  
You know that with new president, you simply create a one to one copy of the objects in the data.presidents array? Unless you have any methods defined on president.prototype, this is unnecessary. With the code you have shown, you could simply do myPres = data.presidents; and you would get the same result. –  Felix Kling May 6 '12 at 16:30
 
@FelixKling thanks for the heads up. –  MDMarra May 6 '12 at 16:33

2 Answers

up vote 3 down vote accepted

Placing the document.write after //end getJSON means it will run before the JSON is retrieved.

The anonymous function you pass to .getJSON is called when the data comes back from the server. If you run the document.write after the //end getJSON it is called before the request comes back.

share|improve this answer
 
+1 It would be good to add an explanation of the "success" callback function to your answer though. –  Paulpro May 6 '12 at 16:25
 
Yes, slow typing = me. –  joshp May 6 '12 at 16:26
 
Is there something that I can do to "wait" for that request to complete, or should I just put whatever code I need that uses that data inside of //end getJSON? I'm pretty new to JS/JQuery. –  MDMarra May 6 '12 at 16:30
 
That function "inside //end getJSON" is the mechanism for waiting. Anything you put in there runs after data is returned. If you need the data after that for a long time, you might want to store it somewhere else. –  joshp May 6 '12 at 16:34
 
Ah, I see. Got it. Thanks –  MDMarra May 6 '12 at 16:36
up vote 0 down vote

I don't like jQuery's $.each() I would do it like this:

function parseJSON(JSONObj){
    var array=new Array();
    var count=0;
    for(var Obj in JSONObj){
        array[count]=JSONObj[Obj];
        count++;
    }
}

Please tell me if it is anything else you wanted

share|improve this answer
 
Seems like in this case (as pointed out in the comment), .each() or any other loop is extemporaneous. Just for my own knowledge, is there a compelling reason not to use $.each() other than the fact that you don't like it? –  MDMarra May 6 '12 at 17:02
1  
@MDMarra: there is actually a good reason to not use this option and use $.each() instead. –  DCoder May 6 '12 at 17:05

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