Why don't parameters retain their value outside of a function?
This question already has an answer here:
What is the explanation for this weird behavior?
Because in Javascript variables are function scoped.
You never passed a and b to myTest method. You passed 8 and 5, so a and b which were part of myTest signature got new scope. a became 8 and b became 5 inside myTest .
Values of a and b inside myTest will not be used outside since their scope is limited to myTest.
Inside your function, you have a local a parameter. So any changes you make to that value, they will not reflect your globally defined a . Since you did not create a c variable or parameter inside the function, you will be changing the global c value.
var c = 0; // Global c
var a = 0; // Global a
var b = myTest(8, 5); // Store the value of the local a from the function return.
function myTest(a,b) {
console.log(a); // This a is a local reference (8)
a++; // Increment local a
c++; // Increment global c
console.log(a); // Print local a (9)
return a; // Return local a
}
console.log(a); // Print global a (0)
console.log(c); // Print global c (1)
console.log(b); // Print returned value (9)上一篇: Javascript自动getter / setters（John Resig Book）
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