This question already has answers here:
Logical operators in JavaScript — how do you use them?
(2 answers)
What does the construct x = x || y mean?
(12 answers)
JavaScript OR (||) variable assignment explanation
(12 answers)
What does the comma operator do in JavaScript?
(5 answers)
Closed 13 days ago.
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I am having trouble understanding this code
let txCount = transActions.reduce((count, item) => (count[item] = count[item] + 1 || 1, count), {});
I understand it is using the logical OR expression but what is "1,count" doing here and why does it work?
(count[item] = count[item] + 1 || 1, count)
Related
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What does this symbol mean in JavaScript?
(1 answer)
What's the meaning of "=>" (an arrow formed from equals & greater than) in JavaScript?
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Closed 2 years ago.
I m trying to picture this or trying to understand this but have a question whose answers i cannot find
const csv_to_array = (data, delimiter = ',', omitFirstRow = false) =>
.slice(omitFirstRow ? data.indexOf('\n') + 1 : 0)
.split('\n')
.map(v => v.split(delimiter));//Please explain this v thing thats confusing for me
console.log(csv_to_array('a,b\nc,d'));
Please help me in this case
This question already has answers here:
What is the explanation for these bizarre JavaScript behaviours mentioned in the 'Wat' talk for CodeMash 2012?
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Why does !{}[true] evaluate to true in JavaScript?
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When does JS interpret {} as an empty block instead of an empty object?
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Closed 3 years ago.
Why does {a:1}['a'] equals ['a'] and console.log( {a:1}['a'] ) equals 1?
I tried in node 13.8 and chrome.
This question already has answers here:
What does the comma operator do in JavaScript?
(5 answers)
What does this symbol mean in JavaScript?
(1 answer)
Using &&'s short-circuiting as an if statement?
(6 answers)
Closed 4 years ago.
I have javascript code and I found the following line :
I'm a bit confused about the syntax
e = k.attr("data-icon"), e && (a.icon = e),
I understand the first part : k.attr("data-icon") but not the rest.
Can any one tell me what does that mean please ?
cheers,
This question already has answers here:
Why use !! to coerce a variable to boolean for use in a conditional expression?
(3 answers)
What is the difference between if(!!condition) and if(condition)
(3 answers)
Why use if (!!err)?
(3 answers)
Closed 5 years ago.
I noticed my colleagues are writing code with double negation in conditions, for example:
else if(colType == 'link'){
value = !!data ? $(data).attr('href') : '';
}
In cases like this, is there a chance that the boolean result of data can be different from !!data?
This question already has answers here:
What does the comma operator do in JavaScript?
(5 answers)
Closed 8 years ago.
What is comma operator in JavaScript. If I execute
var a = 1;
var b = 2;
a,b
I get
2
The comma operator evaluates each of its operands (from left to right)
and returns the value of the last operand.
From: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Comma_Operator
More on: http://javascriptweblog.wordpress.com/2011/04/04/the-javascript-comma-operator/