Today #Day125 of #365DaysOfCode, Learning Essential JavaScript Interview Questions.
17. What will be the output when the following code is executed? Explain.
console.log(false == '0') // true
console.log(false === '0') // false
triple-equal operator === behaves like any traditional equality operator would: evaluates to true if the two expressions on either of its sides have the same type and the same value.
The double-equal operator ==, however, tries to coerce the values before comparing them.
It is therefore generally good practice to use the === rather than ==.
The same holds true for !== vs !=.
18. What is the output out of the following code? Explain your answer.
var a={},
b={key:'b'},
c={key:'c'};
a[b]=123;
a[c]=456;
console.log(a[b]);
The output of this code will be 456 (not 123).
The reason for this is as follows:
When setting an object property, JavaScript will implicitly stringify the parameter value.
In this case, since b and c are both objects, they will both be converted to "[object Object]".
As a result, a[b] anda[c] are both equivalent to a["[object Object]"] and can be used interchangeably.
Therefore, setting or referencing a[c] is precisely the same as setting or referencing a[b].
Conclusion
Learned and practiced Essential JavaScript Interview Questions involving topics like triple-equal operator and double-equal operator and object.
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