Do you understand js implicit type conversion?
Maybe the writing is not very clear, the logic is not very strict, and there are some mistakes. I hope you can criticize and correct me, and I will correct it in time. I am also writing this article as a learner, reversely recording the process of my own learning and exploration, not pointing out the country, slamming Fang Qiu, supercilious masters, if the writing is not good, I hope you will forgive me.
Come and take a look at the following contact questions to see if you can
var str = false + 1
console.lgo(str);
var demo = false == 1;
console.log(demo);The first two should be able to do it. If you can’t do it; I advise you to go back and review the type conversion.
str prints 1
When performing calculations here, false is first converted into a number and then added, and the false conversion digit is 0, so 1 + 0 = 1
demo prints false
The test here is the same false conversion digit is 0; 0 != 1 The two == here can only return false or true, so it is false
The following questions have a certain degree of difficulty; but they are not very difficult. It can still be done if you do it well.
come see the first one
if (typeof(a) && -true + (+undefined) + " ") {
console.log('基础很好');
}Here I want to talk about a knowledge point, a very small knowledge point; it is an undeclared variable that will not report an error only in typeof, just remember it
So typeof(a) returns "undefined" for strings
Converted to a Boolean value is true; undefined here is the undefined of the string, so it is true+undefined converted to a number is nan
Then -1 plus NaN is equal to NaN; any number plus NaN is equal to NaN; then NaN is equal to NaN of a string when adding an empty string. Is this "NaN"
Converted to a Boolean value is true
Tell a point of knowledge
That is, which types convert boolean values to false; except for the following values;
undefined 、null 、false、 ""、 0、 NaN
Remember this time and don't forget it again, only these few values are flase during boolean type conversion; the rest are all true.
Look at the second question
if (11 + '11' * 2 == 33) {
console.log('基础很好');
}Then '11' * 2 here; when performing calculations; because 11 is 11 of a string, it will be converted into 11 of a number before the operation is performed. So 33 is a number type so it can be printed
If you can do a question, you have a good grasp of type conversion; come on ヾ(◍°∇°◍)ﾉﾞ
!!" " + !!"" - !!false || console('可以打印嘛？');The above knowledge points are used again here.
" " This conversion into a boolean value is true! This means negation, right? Then the two negations are themselves;
then the next ""
This is a string pair with nothing; so the conversion to boolean is false
True plus false is converted into a number, whether it is 0 + 1 or 1; and then converted into a Boolean value is true;
&& || has the function of interrupting even && returns when it encounters false
And || returns when it encounters true and does not execute the following code
How is it very simple? did you make it