word-break

значения свойства:

css/style.css

div {
 width: 300px;
 height: 70px;
 border: 1px solid #8E8E8E;
}

.a {
 word-break: normal;
}

.c {
 white-space: pre;
}

index.html

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>New Page</title>
<link href="css/style.css" rel="stylesheet" />
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
</head>
<body>
<div class="a">
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
</div>
<br />
<div id="div1">
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
</div>
<br />
<div class="b">
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
</div>
<script>
/*JavaScript*/
document.getElementById("div1").style.wordBreak = "break-all";
/*jQuery*/
$(document).ready(function () {
$(".b").css({ "word-break": "hyphenate" });
});
</script>
</body>
</html>

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>New Page</title>
<link href="css/style.css" rel="stylesheet" />
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
</head>
<body>
<div class="a">
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
</div>
<br />
<div id="div1">
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
</div>
<br />
<div class="b">
aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
</div>
<script>
/*JavaScript*/
document.getElementById("div1").style.wordBreak = "break-all";
/*jQuery*/
$(document).ready(function () {
$(".b").css({ "word-break": "hyphenate" });
});
</script>
</body>
</html>