Javascript ternary operator -- what is the condition?

user_4347684 0
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I read a handful of SOF posts on ternary operators but I'm still confused with this example:

var str = "I want to count";
var counts = {};
var ch, index, len, count;

for (index = 0; index < str.length; ++index) {
    ch = str.charAt(index); 
    count = counts[ch];
    counts[ch] = count ? count + 1 : 1; // TERNARY
}

I know the syntax is condition ? expression1 : expression2

But I am trying to practice and break up the ternary into an if-else.

I don't know what the condition is supposed to be

counts[ch] = count // this isn't a condition, it's assigning a value...

conditional-operator javascript
2 Answers

The ternary

counts[ch] = count ? count + 1 : 1;

The condition in this expression is not counts[ch] = count but just count and is equivalent to

if (count){
    counts[ch] = count + 1;
}
else {
    counts[ch] = 1;
}

The right hand side of an assignment expression is always evaluated first and the counts[ch] is assigned the result of count ? count + 1 ? 1.

user_5929580

You're conflating the ternary with the assignment expression.

The code

counts[ch] = count ? count + 1 : 1;

can also be written as

counts[ch] = (count ? count + 1 : 1);
// but not (counts[ch] = count) ? count + 1 : 1
// that does something entirely different

And then, writing the matching if/else becomes pretty clear

if (count) {
   counts[ch] = count + 1;
} else {
   counts[ch] = 1;
}
user_52986960
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