Javascript loops and values -

my book says , i'm not entirely sure means. says make sure loop executes properly, need include code change value of conditional expression? mean? correct? may reading wrong when have basic javascript loop

 if(contactscount > 0) {         (i = 0; < contactscount; = + 1){             var item = object[i],                name = item.name,                email = item.email;            target.innerhtml += '<p><a href=mailto:' + email + '">' + name + '</a>!</p>; } } })(); 

surely aren't changing values make work? i'm new i'm kind of clueless.

...you need include code change value of conditional expression? mean?

that bad idea:

var = 0; while (i < 10) {     dosomething(i); } 

why? because loop never end. i's value never changed. endless loops classic form of bug.

so book saying must provide way loop condition (i < 10) change (e.g., modifying i's value).

a bit of tangent, but:

sometimes see loops condition seemingly can't change, e.g.:

while (true) {     // ... } 

if find reaching that, stop , try find better way. there rare use cases above, this:

while (true) {     dothis();     dothat();     if (somecondition) {         break;     }     doanotherthing(); } 

...so in case, controlling condition in middle, , 1 in looping statement isn't condition. poor practice, in very rare situations can right thing do.

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it says can have other statements on same line "if statement", right?

yes, is. javascript doesn't care lines at all (except when it's doing form of error-correction called automatic semicolon insertion; lines matter because linebreaks stand in semicolons part of error-correction algorithm). of these valid , same thing:

// 1 if (a < b) {     alert("a less b");     foo(); } // 2 if (a < b) { alert("a less b"); foo(); } // 3 if (a < b) {     alert("a less b");     foo(); } // 4 if (a < b) { alert("a less b");   foo; } 

because javascript doesn't care lines @ all, they're matter of style.

by far, common style above #1.

separately, if have single statement in control-flow statement's body, block (the {...}) optional. these same thing:

// 1 if (a < b) {     alert("a less b"); } // 2 if (a < b)      alert("a less b"); // 3 if (a < b) alert("a less b"); 

so using {...} single statement in body also, technically, matter of style. in practice, however, using blocks leads fewer bugs in code. if leave off blocks, will bite when add second statement , forget add block:

if (a < b)      alert("a less b");     foo(); 

in above, foo() always called, because it's not in body of if. code this:

if (a < b) {     alert("a less b"); } foo();