如何使用JS动态修改网页源代码?

如

<button class="button2aDis ng-scope" id="tj_a" ng-click="makeComment(pqlist, pap);" ng-if="(pap.checkpoint ? pap.checkpoint : 1) != (shutNum?shutNum:1)" disabled="disabled">下一关</button>

改为

<button class="button2a ng-scope" id="tj_a" ng-click="makeComment(pqlist, pap);" ng-if="(pap.checkpoint ? pap.checkpoint : 1) != (shutNum?shutNum:1)">下一关</button>