Compare equal dates in javascript

Question

With reference to these two questions:

• Simple comparison between dates

• How to compare two dates in Javascript or jQuery

I need to compare the dates and I need three distinctions between two dates, she being equal or greater or minor See the example below:

function gerarData(str) {
    var partes = str.split("/");
    return new Date(partes[2], partes[1] - 1, partes[0]);
}

function teste(){
    var data_1 = '03/03/2016';
    var data_2 = '03/03/2016';

    console.log( gerarData(data_1) );
    console.log( gerarData(data_2) );

    if ( gerarData(data_1) === gerarData(data_2) ) {
      alert("Datas iguais com ===");
    }
    else if ( gerarData(data_1) == gerarData(data_2) ) {
      alert("Datas iguais com ==");
    }
    else if ( gerarData(data_1) > gerarData(data_2) ){
      alert("data_1 > data_2");
    } 
    else if ( gerarData(data_1) < gerarData(data_2) ) {
      alert("data_1 < data_2");
    }
    else{
      alert("inconclusivo \n data_1="+gerarData(data_1)+" \n data_2="+gerarData(data_2));      
    }

}
teste();

Why even the console.log showing me that they are equal he does not enter the condition that makes this check?

Answer 1

In Javascript dates are objects and two different objects are never equal.

Hence new Date(1456959600000) == new Date(1456959600000) (using == or ===) always gives false.

To compare dates can convert the date to Timestamp and in that case the comparison above would be true. In other words, it would compare numbers, the number of milliseconds of the respective date. In practice it would be:

+new Date(1456959600000) == +new Date(1456959600000)

which is basically the same as

1456959600000 == 1456959600000

An example of code could be:

function gerarData(str) {
    var partes = str.split("/");
    return +new Date(partes[2], partes[1] - 1, partes[0]);
}

function teste(data_1, data_2) {
    var a = gerarData(data_1);
    var b = gerarData(data_2);

    var tipo;
    if (a < b) tipo = 'anterior';
    else if (a == b) tipo = 'igual';
    else if (a > b) tipo = 'posterior';
    else tipo = 'inconclusivo'
    return tipo;
}

jsFiddle: https://jsfiddle.net/grggk9xb/

About the +:

In the background use +new Date(); or use new Date().getTime(); generates a number, timestamp. The reason why + works here is because it does a type conversion of the date object to a number. It is called unit operator (or unary?), in English unary plus operator and what it does is convert what is after it to a numerical value. In the case of the date it does this by invoking the .valueOf(), but can also be used in Strings with numbers, or boolean. Some examples:

+true // 1 +false // 0 +'20' // 20 +'45deg' // Nan (in this case mixing letters it does not find numerical value, parseint would be an alternative)

Interesting reading on the + ^{(in English)}:

• unary add
• plus Sign javascript

Answer 2

You need to use the getTime() function to convert to numbers, so that you enter the correct condition.

Example:

function gerarData(str) {
      var partes = str.split("/");
      return new Date(partes[2], partes[1] - 1, partes[0]).getTime();
}

function teste() {
  var data_1 = '03/03/2016';
  var data_2 = '03/03/2016';
  if (gerarData(data_1) === gerarData(data_2)) {
    alert("Datas iguais com ===");
  } else if (gerarData(data_1) == gerarData(data_2)) {
    alert("Datas iguais com ==");
  } else if (gerarData(data_1) > gerarData(data_2)) {
    alert("data_1 > data_2");
  } else if (gerarData(data_1) < gerarData(data_2)) {
    alert("data_1 < data_2");
  } else {
    alert("inconclusivo \n data_1=" + gerarData(data_1) + " \n data_2=" + gerarData(data_2));
  }

}
teste();