Question

在javascript中,如果没有任何内容的话,我想作一个其他发言,将内容价值(案文领域以html的形式)改为零。我有:

if(document.getElementById( dollarinput ).value == null){
    var dollars = 0;
}
else{
    var dollars = parseInt(document.getElementById( dollarinput ).value);
}

Something isn t working correctly in the if condition, but I m not sure what I did wrong.

Answer 1

您需要将变式声明移至if,并核对空字,如:

var dollars;
if(document.getElementById( dollarinput ).value ==   ){
    dollars = 0;
}
else{
    dollars = parseInt(document.getElementById( dollarinput ).value);
}

Answer 2

Value of an input can never be null ! if there is no value, it will be an empty string.
alert( == null); // false

<Fixed Code:

if(document.getElementById( dollarinput ).value){
    var dollars = 0;
}
else{
    var dollars = parseInt(document.getElementById( dollarinput ).value);
}

Answer 3

var dollars = 0;
var dollarinput = document.getElementById( dollarinput );
if( ! dollarinput.length )
{
    dollars = parseInt(dollarinput.value);
}

Answer 4

Check if it s an empty string instead:

if(document.getElementById( dollarinput ).value ==   ){
    var dollars = 0;
} else{
    var dollars = parseInt(document.getElementById( dollarinput ).value, 10);
}

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