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parameter, also can be understood as an expression, the parameter is used when the equivalent assignment
var a=1;
function Fn1 (a) {//Here the parameter a equals: var a = 1; A is undefined and becomes 1, here the variable is a local variable, with the outside Var a=1;
alert (a); 1 Here is the local variable;
a=2;
}
FN1 (a);
alert (a); 1 because the A in here is still access to global variables;
To get the value inside a function:
Method one: Through the scope chain, reverse access; global variables;
var str = ';
function fn1 () {
var a= ' Awuawu ~ ';
str = A;
}
FN1 ();
alert (str); At this point the value of STR is a;
Method Two: pass through the parameter;
function fn2 () {
var a= ' free ~ ';
Fn3 (a);
}
FN2 ();
function Fn3 (a) {//Here is not a above, can also be b,c ... Used to receive the pass of a function
alert (a);
}
Second: if judgment, for loop is not scope, and function is not the same, but use time to be particularly careful;
First parse, then execute, is the scope of the flag; so the function is a scope; but the if,for is not a scope;
For compatibility reasons, when you want to define global variables, or global functions, put them outside the if,for, etc.
The FOR function does not use the defined variable i directly, otherwise there will be a hidden danger (we should be very careful when using the For loop, put in a different position, may be different values)
For example:
1 <!DOCTYPE HTML>2 <HTML>3 <Head>4 <Metahttp-equiv= "Content-type"content= "text/html; charset=utf-8">5 <title>Untitled Document</title>6 7 8 9 </Head>Ten One <Body> A - <inputtype= "button"value= "Button 1"> - <inputtype= "button"value= "button 2"> the <inputtype= "button"value= "button 3"> - - <Script> - + varabtn=document.getElementsByTagName ('input'); - + for( varI=0; I<Abtn.length;i++){ A at Abtn[i].onclick= function(){ - - //alert (i);//return 3; - //abtn[i].style.background = ' blue ';//Click the button at this time, there will be no response and error, because at this time I has been three times since the increase, became 3; Abtn[3] does not exist at all; - for( varI=0; I<abtn.length; I++){ - Abtn[i].style.background= 'Blue'; in } - to } + - } the </Script> * </Body> $ </HTML>
Scope 2-js Learning note 2015-6-10 (54th day)
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