javascript - Accessing global variable defined inside a function -

i trying understand variable scopes in javascript , friend asked me question. use here.

function abc(){   var = b = 10; // local, b global variable. right?   c = 5; // c global variable } d = 20; // d global variable  console.log(b); // b not defined error. why? isn't b global variable? console.log(c); // again, why 'c not defined'. 

i ran code in chrome console. shouldn't expect 10 , 5 in console? gives 'b not defined', 'c not defined' error instead. why happen if b, c global variables? console.log(d) works fine.

here's fiddle.

why happen if b, c global variables?

b , c created if call abc. merely defining function not magically execute body.

function abc(){   var = b = 10; // local, b global variable.   c = 5; // c global variable }  // call abc execute statements inside function abc();  console.log(b); // 10 console.log(c); // 5 

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that said, implicitly creating global variables not still. avoid globals if possible, , if not, explicitly declare them assigning global object (window in browsers).