We can fix this by defining our variables in the global scope.
<\/p>\n\n\n\n
numA = 1\nnumB = 2\n \nfunction nums() { \n return numA + numB\n}\n \nconsole.log(nums()); \n \n\/\/ returns 3<\/pre><\/div>\n\n\n\nStrict Mode<\/h3>\n\n\n\n
Strict Mode intentionally has a different set of semantics than the regular defaulted, \u201csloppy mode\u201d JavaScript code. A key thing to remember while coding in strict mode is that it eliminates silent errors by changing them into throw errors. A JavaScript statement will be using strict mode if \u201cuse strict\u201d; is invoked before a statement.
<\/p>\n\n\n\n
function referenceErr(a){\n "use strict";\n foo = true;\n \n if(a == 0){\n return foo\n } else {\n return !foo\n }\n \n }\n \n console.log(referenceErr(1))\n \n\/\/ Uncaught ReferenceError: foo is not defined<\/pre><\/div>\n\n\n\nAs JavaScript developers we know to use var, let, or const in order to define a variable, but the above would have been a silent error if strict mode was not invoked.
<\/p>\n\n\n\n
function referenceErr(a){\n "use strict";\n let foo = true;\n \n if(a == 0){\n return foo\n } else {\n return !foo\n }\n \n }\n \n console.log(referenceErr(1))\n\/\/ returns false<\/pre><\/div>\n\n\n\nRedeclarations<\/h3>\n\n\n\n
Not full understanding how to redeclare variables can also trigger reference errors.
<\/p>\n\n\n\n
function redeclarations() {\n let declare = 1;\n if (true) {\n let declare = (declare + 1); \n }\n }\n console.log(redeclarations())\n\/\/ Uncaught ReferenceError: Cannot access 'declare' before initialization<\/pre><\/div>\n\n\n\nTo fix the code above, we must either change \u201clet\u201d to \u201cvar\u201d or omit \u201clet\u201d inside our if statement completely.
<\/p>\n\n\n\n
function redeclarations() {\n let declare = 1;\n if (true) {\n declare = (declare + 1); \n \n }\n }\n console.log(redeclarations())<\/pre><\/div>\n\n\n\n<\/h2>\n\n\n\n